diff --git a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/logging/impl/Log.java b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/logging/impl/Log.java
index 2e06706fd10..a8bd51d8861 100644
--- a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/logging/impl/Log.java
+++ b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/logging/impl/Log.java
@@ -602,7 +602,7 @@ SearchException invalidFieldValueType(@FormatWith(ClassFormatter.class) Class<?>
 	@Message(id = ID_OFFSET + 113,
 			value = "Invalid cardinality for projection on field '%1$s': the projection is single-valued,"
 					+ " but this field is multi-valued."
-					+ " Make sure to call '.multi()' when you create the projection.")
+					+ " Make sure to call '.collector(...)' when you create the projection.")
 	SearchException invalidSingleValuedProjectionOnMultiValuedField(String absolutePath, @Param EventContext context);
 
 	@Message(id = ID_OFFSET + 117,
@@ -732,9 +732,9 @@ SearchException invalidContextForProjectionOnField(String absolutePath,
 			value = "Invalid cardinality for projection on field '%1$s': the projection is single-valued,"
 					+ " but this field is effectively multi-valued in this context,"
 					+ " because parent object field '%2$s' is multi-valued."
-					+ " Either call '.multi()' when you create the projection on field '%1$s',"
+					+ " Either call '.collector(...)' when you create the projection on field '%1$s',"
 					+ " or wrap that projection in an object projection like this:"
-					+ " 'f.object(\"%2$s\").from(<the projection on field %1$s>).as(...).multi()'.")
+					+ " 'f.object(\"%2$s\").from(<the projection on field %1$s>).as(...).collector(...)'.")
 	SearchException invalidSingleValuedProjectionOnValueFieldInMultiValuedObjectField(String absolutePath,
 			String objectFieldAbsolutePath);
 
diff --git a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/highlighter/impl/ElasticsearchSearchHighlighter.java b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/highlighter/impl/ElasticsearchSearchHighlighter.java
index 63fdd009066..76b46c8ce91 100644
--- a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/highlighter/impl/ElasticsearchSearchHighlighter.java
+++ b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/highlighter/impl/ElasticsearchSearchHighlighter.java
@@ -14,7 +14,7 @@
 import org.hibernate.search.backend.elasticsearch.search.common.impl.ElasticsearchSearchIndexScope;
 import org.hibernate.search.engine.search.highlighter.SearchHighlighter;
 import org.hibernate.search.engine.search.highlighter.spi.SearchHighlighterType;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.util.common.logging.impl.LoggerFactory;
 
 import com.google.gson.JsonObject;
@@ -31,7 +31,7 @@ public interface ElasticsearchSearchHighlighter extends SearchHighlighter {
 
 	SearchHighlighterType type();
 
-	boolean isCompatible(ProjectionAccumulator.Provider<?, ?> accumulatorProvider);
+	boolean isCompatible(ProjectionCollector.Provider<?, ?> collectorProvider);
 
 	static ElasticsearchSearchHighlighter from(ElasticsearchSearchIndexScope<?> scope, SearchHighlighter highlighter) {
 		if ( !( highlighter instanceof ElasticsearchSearchHighlighter ) ) {
diff --git a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/highlighter/impl/ElasticsearchSearchHighlighterImpl.java b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/highlighter/impl/ElasticsearchSearchHighlighterImpl.java
index 131b205ec63..edf56f0a129 100644
--- a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/highlighter/impl/ElasticsearchSearchHighlighterImpl.java
+++ b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/highlighter/impl/ElasticsearchSearchHighlighterImpl.java
@@ -21,7 +21,7 @@
 import org.hibernate.search.engine.search.highlighter.spi.BoundaryScannerType;
 import org.hibernate.search.engine.search.highlighter.spi.SearchHighlighterBuilder;
 import org.hibernate.search.engine.search.highlighter.spi.SearchHighlighterType;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 
 import com.google.gson.JsonArray;
 import com.google.gson.JsonObject;
@@ -143,9 +143,9 @@ public SearchHighlighterType type() {
 	}
 
 	@Override
-	public boolean isCompatible(ProjectionAccumulator.Provider<?, ?> provider) {
-		return !provider.isSingleValued()
-				|| ( provider.isSingleValued() && ( numberOfFragments != null && numberOfFragments.equals( 1 ) ) );
+	public boolean isCompatible(ProjectionCollector.Provider<?, ?> collectorProvider) {
+		return !collectorProvider.isSingleValued()
+				|| ( collectorProvider.isSingleValued() && ( numberOfFragments != null && numberOfFragments.equals( 1 ) ) );
 	}
 
 	private JsonObject toJson(JsonObject result) {
diff --git a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/AccumulatingSourceExtractor.java b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/AccumulatingSourceExtractor.java
index d081666a5d3..471d2432dea 100644
--- a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/AccumulatingSourceExtractor.java
+++ b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/AccumulatingSourceExtractor.java
@@ -12,7 +12,7 @@
 import org.hibernate.search.backend.elasticsearch.gson.impl.JsonElementTypes;
 import org.hibernate.search.backend.elasticsearch.gson.impl.UnexpectedJsonElementTypeException;
 import org.hibernate.search.engine.search.loading.spi.ProjectionHitMapper;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
@@ -24,18 +24,18 @@ abstract class AccumulatingSourceExtractor<E, V, A, P>
 			JsonAccessor.root().property( "_source" ).asArray();
 
 	private final String[] fieldPathComponents;
-	final ProjectionAccumulator<E, V, A, P> accumulator;
+	final ProjectionCollector<E, V, A, P> collector;
 
 	public AccumulatingSourceExtractor(String[] fieldPathComponents,
-			ProjectionAccumulator<E, V, A, P> accumulator) {
+			ProjectionCollector<E, V, A, P> collector) {
 		this.fieldPathComponents = fieldPathComponents;
-		this.accumulator = accumulator;
+		this.collector = collector;
 	}
 
 	@Override
 	public final A extract(ProjectionHitMapper<?> projectionHitMapper, JsonObject hit,
 			JsonObject source, ProjectionExtractContext context) {
-		A accumulated = accumulator.createInitial();
+		A accumulated = collector.createInitial();
 		accumulated = collect( projectionHitMapper, hit, source, context, accumulated, 0 );
 		return accumulated;
 	}
@@ -83,17 +83,17 @@ private A collectTargetField(ProjectionHitMapper<?> projectionHitMapper, JsonObj
 		}
 		else if ( fieldValue.isJsonNull() ) {
 			// Present, but null
-			return accumulator.accumulate( accumulated, extract( projectionHitMapper, hit, fieldValue, context ) );
+			return collector.accumulate( accumulated, extract( projectionHitMapper, hit, fieldValue, context ) );
 		}
 		else if ( !canDecodeArrays() && fieldValue.isJsonArray() ) {
 			for ( JsonElement childElement : fieldValue.getAsJsonArray() ) {
-				accumulated = accumulator.accumulate( accumulated,
+				accumulated = collector.accumulate( accumulated,
 						extract( projectionHitMapper, hit, childElement, context ) );
 			}
 			return accumulated;
 		}
 		else {
-			return accumulator.accumulate( accumulated, extract( projectionHitMapper, hit, fieldValue, context ) );
+			return collector.accumulate( accumulated, extract( projectionHitMapper, hit, fieldValue, context ) );
 		}
 	}
 
diff --git a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchCompositeProjection.java b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchCompositeProjection.java
index 1cada46bdd6..065c138a5d2 100644
--- a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchCompositeProjection.java
+++ b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchCompositeProjection.java
@@ -9,9 +9,9 @@
 import org.hibernate.search.backend.elasticsearch.search.common.impl.ElasticsearchSearchIndexScope;
 import org.hibernate.search.engine.search.loading.spi.LoadingResult;
 import org.hibernate.search.engine.search.loading.spi.ProjectionHitMapper;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.spi.CompositeProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionCompositor;
 
 import com.google.gson.JsonObject;
@@ -31,14 +31,14 @@ class ElasticsearchCompositeProjection<E, V, A, P>
 
 	private final ElasticsearchSearchProjection<?>[] inners;
 	private final ProjectionCompositor<E, V> compositor;
-	private final ProjectionAccumulator<E, V, A, P> accumulator;
+	private final ProjectionCollector<E, V, A, P> collector;
 
 	public ElasticsearchCompositeProjection(Builder builder, ElasticsearchSearchProjection<?>[] inners,
-			ProjectionCompositor<E, V> compositor, ProjectionAccumulator<E, V, A, P> accumulator) {
+			ProjectionCompositor<E, V> compositor, ProjectionCollector<E, V, A, P> collector) {
 		super( builder.scope );
 		this.inners = inners;
 		this.compositor = compositor;
-		this.accumulator = accumulator;
+		this.collector = collector;
 	}
 
 	@Override
@@ -46,7 +46,7 @@ public String toString() {
 		return getClass().getSimpleName() + "["
 				+ "inners=" + Arrays.toString( inners )
 				+ ", compositor=" + compositor
-				+ ", accumulator=" + accumulator
+				+ ", collector=" + collector
 				+ "]";
 	}
 
@@ -71,21 +71,21 @@ public String toString() {
 			return getClass().getSimpleName() + "["
 					+ "inners=" + Arrays.toString( inners )
 					+ ", compositor=" + compositor
-					+ ", accumulator=" + accumulator
+					+ ", collector=" + collector
 					+ "]";
 		}
 
 		@Override
 		public A extract(ProjectionHitMapper<?> projectionHitMapper, JsonObject hit,
 				JsonObject source, ProjectionExtractContext context) {
-			A accumulated = accumulator.createInitial();
+			A accumulated = collector.createInitial();
 
 			E components = compositor.createInitial();
 			for ( int i = 0; i < inners.length; i++ ) {
 				Object extractedDataForInner = inners[i].extract( projectionHitMapper, hit, source, context );
 				components = compositor.set( components, i, extractedDataForInner );
 			}
-			accumulated = accumulator.accumulate( accumulated, components );
+			accumulated = collector.accumulate( accumulated, components );
 
 			return accumulated;
 		}
@@ -93,8 +93,8 @@ public A extract(ProjectionHitMapper<?> projectionHitMapper, JsonObject hit,
 		@Override
 		public final P transform(LoadingResult<?> loadingResult, A accumulated,
 				ProjectionTransformContext context) {
-			for ( int i = 0; i < accumulator.size( accumulated ); i++ ) {
-				E transformedData = accumulator.get( accumulated, i );
+			for ( int i = 0; i < collector.size( accumulated ); i++ ) {
+				E transformedData = collector.get( accumulated, i );
 				// Transform in-place
 				for ( int j = 0; j < inners.length; j++ ) {
 					Object extractedDataForInner = compositor.get( transformedData, j );
@@ -103,9 +103,9 @@ public final P transform(LoadingResult<?> loadingResult, A accumulated,
 					transformedData = compositor.set( transformedData, j, transformedDataForInner );
 				}
 
-				accumulated = accumulator.transform( accumulated, i, compositor.finish( transformedData ) );
+				accumulated = collector.transform( accumulated, i, compositor.finish( transformedData ) );
 			}
-			return accumulator.finish( accumulated );
+			return collector.finish( accumulated );
 		}
 	}
 
@@ -119,14 +119,14 @@ static class Builder implements CompositeProjectionBuilder {
 
 		@Override
 		public <E, V, P> SearchProjection<P> build(SearchProjection<?>[] inners, ProjectionCompositor<E, V> compositor,
-				ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
+				ProjectionCollector.Provider<V, P> collectorProvider) {
 			ElasticsearchSearchProjection<?>[] typedInners =
 					new ElasticsearchSearchProjection<?>[inners.length];
 			for ( int i = 0; i < inners.length; i++ ) {
 				typedInners[i] = ElasticsearchSearchProjection.from( scope, inners[i] );
 			}
 			return new ElasticsearchCompositeProjection<>( this, typedInners,
-					compositor, accumulatorProvider.get() );
+					compositor, collectorProvider.get() );
 		}
 	}
 }
diff --git a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchDistanceToFieldProjection.java b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchDistanceToFieldProjection.java
index 6df42ab7423..79a9920256e 100644
--- a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchDistanceToFieldProjection.java
+++ b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchDistanceToFieldProjection.java
@@ -18,9 +18,9 @@
 import org.hibernate.search.engine.backend.types.converter.spi.ProjectionConverter;
 import org.hibernate.search.engine.search.loading.spi.LoadingResult;
 import org.hibernate.search.engine.search.loading.spi.ProjectionHitMapper;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.spi.DistanceToFieldProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.spatial.DistanceUnit;
 import org.hibernate.search.engine.spatial.GeoPoint;
 
@@ -62,14 +62,14 @@ public class ElasticsearchDistanceToFieldProjection<A, P> extends AbstractElasti
 	private final GeoPoint center;
 	private final DistanceUnit unit;
 
-	private final ProjectionAccumulator<Double, Double, A, P> accumulator;
+	private final ProjectionCollector<Double, Double, A, P> collector;
 
 	private final String scriptFieldName;
 	private final ElasticsearchFieldProjection<?, Double, P, ?> sourceProjection;
 
 	private ElasticsearchDistanceToFieldProjection(Builder builder,
-			ProjectionAccumulator.Provider<Double, P> accumulatorProvider,
-			ProjectionAccumulator<Double, Double, A, P> accumulator) {
+			ProjectionCollector.Provider<Double, P> collectorProvider,
+			ProjectionCollector<Double, Double, A, P> collector) {
 		super( builder );
 		this.codec = builder.field.type().codec();
 
@@ -77,7 +77,7 @@ private ElasticsearchDistanceToFieldProjection(Builder builder,
 		this.singleValuedInRoot = !builder.field.multiValuedInRoot();
 		this.center = builder.center;
 		this.unit = builder.unit;
-		this.accumulator = accumulator;
+		this.collector = collector;
 		if ( singleValuedInRoot && builder.field.nestedPathHierarchy().isEmpty() ) {
 			// Rely on docValues when there is no sort to extract the distance from.
 			scriptFieldName = createScriptFieldName( absoluteFieldPath, center );
@@ -88,7 +88,7 @@ private ElasticsearchDistanceToFieldProjection(Builder builder,
 			scriptFieldName = null;
 			this.sourceProjection = new ElasticsearchFieldProjection<>(
 					builder.scope, builder.field,
-					this::computeDistanceWithUnit, false, NO_OP_DOUBLE_CONVERTER, accumulatorProvider
+					this::computeDistanceWithUnit, false, NO_OP_DOUBLE_CONVERTER, collectorProvider
 			);
 		}
 	}
@@ -99,7 +99,7 @@ public String toString() {
 				+ "absoluteFieldPath=" + absoluteFieldPath
 				+ ", center=" + center
 				+ ", unit=" + unit
-				+ ", accumulator=" + accumulator
+				+ ", collector=" + collector
 				+ "]";
 	}
 
@@ -130,13 +130,13 @@ public A extract(ProjectionHitMapper<?> projectionHitMapper, JsonObject hit,
 		Integer distanceSortIndex = singleValuedInRoot ? context.getDistanceSortIndex( absoluteFieldPath, center ) : null;
 
 		if ( distanceSortIndex != null ) {
-			A accumulated = accumulator.createInitial();
-			accumulated = accumulator.accumulate( accumulated, extractDistanceFromSortKey( hit, distanceSortIndex ) );
+			A accumulated = collector.createInitial();
+			accumulated = collector.accumulate( accumulated, extractDistanceFromSortKey( hit, distanceSortIndex ) );
 			return accumulated;
 		}
 		else {
-			A accumulated = accumulator.createInitial();
-			accumulated = accumulator.accumulate( accumulated, extractDistanceFromScriptField( hit ) );
+			A accumulated = collector.createInitial();
+			accumulated = collector.accumulate( accumulated, extractDistanceFromScriptField( hit ) );
 			return accumulated;
 		}
 	}
@@ -145,7 +145,7 @@ public A extract(ProjectionHitMapper<?> projectionHitMapper, JsonObject hit,
 	public P transform(LoadingResult<?> loadingResult, A extractedData,
 			ProjectionTransformContext context) {
 		// Nothing to transform: we take the values as they are.
-		return accumulator.finish( extractedData );
+		return collector.finish( extractedData );
 	}
 
 	private Double extractDistanceFromScriptField(JsonObject hit) {
@@ -255,9 +255,9 @@ public void unit(DistanceUnit unit) {
 		}
 
 		@Override
-		public <P> SearchProjection<P> build(ProjectionAccumulator.Provider<Double, P> accumulatorProvider) {
-			return new ElasticsearchDistanceToFieldProjection<>( this, accumulatorProvider,
-					accumulatorProvider.get() );
+		public <P> SearchProjection<P> build(ProjectionCollector.Provider<Double, P> collectorProvider) {
+			return new ElasticsearchDistanceToFieldProjection<>( this, collectorProvider,
+					collectorProvider.get() );
 		}
 	}
 }
diff --git a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchFieldHighlightProjection.java b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchFieldHighlightProjection.java
index 99002c18c63..b748dee288b 100644
--- a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchFieldHighlightProjection.java
+++ b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchFieldHighlightProjection.java
@@ -19,9 +19,9 @@
 import org.hibernate.search.engine.search.highlighter.spi.SearchHighlighterType;
 import org.hibernate.search.engine.search.loading.spi.LoadingResult;
 import org.hibernate.search.engine.search.loading.spi.ProjectionHitMapper;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.dsl.spi.HighlightProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 
 import com.google.gson.JsonArray;
 import com.google.gson.JsonElement;
@@ -38,23 +38,23 @@ public class ElasticsearchFieldHighlightProjection<T> implements ElasticsearchSe
 
 	private final String highlighterName;
 	private final ElasticsearchSearchIndexValueFieldTypeContext<?> typeContext;
-	private final ProjectionAccumulator.Provider<String, T> accumulatorProvider;
+	private final ProjectionCollector.Provider<String, T> collectorProvider;
 
 	private ElasticsearchFieldHighlightProjection(Builder builder,
-			ProjectionAccumulator.Provider<String, T> accumulatorProvider) {
-		this( builder.scope, builder.field, builder.highlighterName(), accumulatorProvider );
+			ProjectionCollector.Provider<String, T> collectorProvider) {
+		this( builder.scope, builder.field, builder.highlighterName(), collectorProvider );
 	}
 
 	private ElasticsearchFieldHighlightProjection(ElasticsearchSearchIndexScope<?> scope,
 			ElasticsearchSearchIndexValueFieldContext<?> field,
 			String highlighterName,
-			ProjectionAccumulator.Provider<String, T> accumulatorProvider) {
+			ProjectionCollector.Provider<String, T> collectorProvider) {
 		this.indexNames = scope.hibernateSearchIndexNames();
 		this.absoluteFieldPath = field.absolutePath();
 		this.absoluteFieldPathComponents = field.absolutePathComponents();
 		this.highlighterName = highlighterName;
 		this.typeContext = field.type();
-		this.accumulatorProvider = accumulatorProvider;
+		this.collectorProvider = collectorProvider;
 	}
 
 	@Override
@@ -93,7 +93,7 @@ public Extractor<?, T> request(JsonObject requestBody, ProjectionRequestContext
 		if ( !typeContext.highlighterTypeSupported( highlighterType ) ) {
 			throw log.highlighterTypeNotSupported( highlighterType, absoluteFieldPath );
 		}
-		if ( !context.root().isCompatibleHighlighter( highlighterName, accumulatorProvider ) ) {
+		if ( !context.root().isCompatibleHighlighter( highlighterName, collectorProvider ) ) {
 			throw log.highlighterIncompatibleCardinality();
 		}
 
@@ -102,26 +102,26 @@ public Extractor<?, T> request(JsonObject requestBody, ProjectionRequestContext
 				REQUEST_HIGHLIGHT_FIELDS_ACCESSOR.getOrCreate( requestBody, JsonObject::new )
 		);
 
-		return new FieldHighlightExtractor<>( innerContext.absoluteCurrentFieldPath(), accumulatorProvider.get() );
+		return new FieldHighlightExtractor<>( innerContext.absoluteCurrentFieldPath(), collectorProvider.get() );
 	}
 
 	private class FieldHighlightExtractor<A> implements Extractor<A, T> {
 		private final JsonArrayAccessor highlightAccessor;
-		private final ProjectionAccumulator<String, String, A, T> accumulator;
+		private final ProjectionCollector<String, String, A, T> collector;
 
-		private FieldHighlightExtractor(String fieldPath, ProjectionAccumulator<String, String, A, T> accumulator) {
+		private FieldHighlightExtractor(String fieldPath, ProjectionCollector<String, String, A, T> collector) {
 			this.highlightAccessor = JsonAccessor.root().property( "highlight" ).property( fieldPath ).asArray();
-			this.accumulator = accumulator;
+			this.collector = collector;
 		}
 
 		@Override
 		public A extract(ProjectionHitMapper<?> projectionHitMapper, JsonObject hit, JsonObject source,
 				ProjectionExtractContext context) {
-			A initial = accumulator.createInitial();
+			A initial = collector.createInitial();
 			Optional<JsonArray> highlights = highlightAccessor.get( hit );
 			if ( highlights.isPresent() ) {
 				for ( JsonElement element : highlights.get() ) {
-					initial = accumulator.accumulate( initial, element.getAsString() );
+					initial = collector.accumulate( initial, element.getAsString() );
 				}
 			}
 			return initial;
@@ -129,7 +129,7 @@ public A extract(ProjectionHitMapper<?> projectionHitMapper, JsonObject hit, Jso
 
 		@Override
 		public T transform(LoadingResult<?> loadingResult, A extractedData, ProjectionTransformContext context) {
-			return accumulator.finish( extractedData );
+			return collector.finish( extractedData );
 		}
 	}
 
@@ -164,8 +164,8 @@ protected String highlighterName() {
 		}
 
 		@Override
-		public <V> SearchProjection<V> build(ProjectionAccumulator.Provider<String, V> accumulatorProvider) {
-			return new ElasticsearchFieldHighlightProjection<>( this, accumulatorProvider );
+		public <V> SearchProjection<V> build(ProjectionCollector.Provider<String, V> collectorProvider) {
+			return new ElasticsearchFieldHighlightProjection<>( this, collectorProvider );
 		}
 	}
 }
diff --git a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchFieldProjection.java b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchFieldProjection.java
index 7893586ddf2..891d8aec867 100644
--- a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchFieldProjection.java
+++ b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchFieldProjection.java
@@ -17,9 +17,9 @@
 import org.hibernate.search.engine.search.common.ValueModel;
 import org.hibernate.search.engine.search.loading.spi.LoadingResult;
 import org.hibernate.search.engine.search.loading.spi.ProjectionHitMapper;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.spi.FieldProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.util.common.logging.impl.LoggerFactory;
 
 import com.google.gson.JsonElement;
@@ -44,36 +44,37 @@ public class ElasticsearchFieldProjection<F, V, P, T> extends AbstractElasticsea
 	private final Function<JsonElement, T> decodeFunction;
 	private final boolean canDecodeArrays;
 	private final ProjectionConverter<? super T, ? extends V> converter;
-	private final ProjectionAccumulator.Provider<V, P> accumulatorProvider;
+	private final ProjectionCollector.Provider<V, P> collectorProvider;
 
 	private ElasticsearchFieldProjection(Builder<F, V, T> builder,
-			ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
+			ProjectionCollector.Provider<V, P> collectorProvider) {
 		this( builder.scope, builder.field, builder.decodeFunction, builder.canDecodeArrays, builder.converter,
-				accumulatorProvider );
+				collectorProvider
+		);
 	}
 
 	ElasticsearchFieldProjection(ElasticsearchSearchIndexScope<?> scope,
 			ElasticsearchSearchIndexValueFieldContext<?> field,
 			Function<JsonElement, T> decodeFunction, boolean canDecodeArrays,
 			ProjectionConverter<? super T, ? extends V> converter,
-			ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
+			ProjectionCollector.Provider<V, P> collectorProvider) {
 		super( scope );
 		this.absoluteFieldPath = field.absolutePath();
 		this.absoluteFieldPathComponents = field.absolutePathComponents();
-		this.requiredContextAbsoluteFieldPath = accumulatorProvider.isSingleValued()
+		this.requiredContextAbsoluteFieldPath = collectorProvider.isSingleValued()
 				? field.closestMultiValuedParentAbsolutePath()
 				: null;
 		this.decodeFunction = decodeFunction;
 		this.canDecodeArrays = canDecodeArrays;
 		this.converter = converter;
-		this.accumulatorProvider = accumulatorProvider;
+		this.collectorProvider = collectorProvider;
 	}
 
 	@Override
 	public String toString() {
 		return getClass().getSimpleName() + "["
 				+ "absoluteFieldPath=" + absoluteFieldPath
-				+ ", accumulatorProvider=" + accumulatorProvider
+				+ ", collectorProvider=" + collectorProvider
 				+ "]";
 	}
 
@@ -87,22 +88,22 @@ public ValueFieldExtractor<?> request(JsonObject requestBody, ProjectionRequestC
 		}
 		JsonPrimitive fieldPathJson = new JsonPrimitive( absoluteFieldPath );
 		AccumulatingSourceExtractor.REQUEST_SOURCE_ACCESSOR.addElementIfAbsent( requestBody, fieldPathJson );
-		return new ValueFieldExtractor<>( innerContext.relativeCurrentFieldPathComponents(), accumulatorProvider.get() );
+		return new ValueFieldExtractor<>( innerContext.relativeCurrentFieldPathComponents(), collectorProvider.get() );
 	}
 
 	/**
 	 * @param <A> The type of the temporary storage for accumulated values, before and after being transformed.
 	 */
 	private class ValueFieldExtractor<A> extends AccumulatingSourceExtractor<T, V, A, P> {
-		public ValueFieldExtractor(String[] fieldPathComponents, ProjectionAccumulator<T, V, A, P> accumulator) {
-			super( fieldPathComponents, accumulator );
+		public ValueFieldExtractor(String[] fieldPathComponents, ProjectionCollector<T, V, A, P> collector) {
+			super( fieldPathComponents, collector );
 		}
 
 		@Override
 		public String toString() {
 			return getClass().getSimpleName() + "["
 					+ "absoluteFieldPath=" + absoluteFieldPath
-					+ ", accumulator=" + accumulator
+					+ ", collector=" + collector
 					+ "]";
 		}
 
@@ -121,8 +122,8 @@ protected boolean canDecodeArrays() {
 		public P transform(LoadingResult<?> loadingResult, A extractedData,
 				ProjectionTransformContext context) {
 			FromDocumentValueConvertContext convertContext = context.fromDocumentValueConvertContext();
-			A transformedData = accumulator.transformAll( extractedData, converter, convertContext );
-			return accumulator.finish( transformedData );
+			A transformedData = collector.transformAll( extractedData, converter.delegate(), convertContext );
+			return collector.finish( transformedData );
 		}
 	}
 
@@ -193,11 +194,11 @@ private Builder(Function<JsonElement, T> decodeFunction, boolean canDecodeArrays
 		}
 
 		@Override
-		public <P> SearchProjection<P> build(ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
-			if ( accumulatorProvider.isSingleValued() && field.multiValued() ) {
+		public <P> SearchProjection<P> build(ProjectionCollector.Provider<V, P> collectorProvider) {
+			if ( collectorProvider.isSingleValued() && field.multiValued() ) {
 				throw log.invalidSingleValuedProjectionOnMultiValuedField( field.absolutePath(), field.eventContext() );
 			}
-			return new ElasticsearchFieldProjection<>( this, accumulatorProvider );
+			return new ElasticsearchFieldProjection<>( this, collectorProvider );
 		}
 	}
 }
diff --git a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchObjectProjection.java b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchObjectProjection.java
index 46f0826a4f7..50f4e99642a 100644
--- a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchObjectProjection.java
+++ b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ElasticsearchObjectProjection.java
@@ -11,9 +11,9 @@
 import org.hibernate.search.backend.elasticsearch.search.common.impl.ElasticsearchSearchIndexScope;
 import org.hibernate.search.engine.search.loading.spi.LoadingResult;
 import org.hibernate.search.engine.search.loading.spi.ProjectionHitMapper;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.spi.CompositeProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionCompositor;
 
 import com.google.gson.JsonElement;
@@ -37,19 +37,19 @@ public class ElasticsearchObjectProjection<E, V, P>
 	private final String requiredContextAbsoluteFieldPath;
 	private final ElasticsearchSearchProjection<?>[] inners;
 	private final ProjectionCompositor<E, V> compositor;
-	private final ProjectionAccumulator.Provider<V, P> accumulatorProvider;
+	private final ProjectionCollector.Provider<V, P> collectorProvider;
 
 	public ElasticsearchObjectProjection(Builder builder, ElasticsearchSearchProjection<?>[] inners,
-			ProjectionCompositor<E, V> compositor, ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
+			ProjectionCompositor<E, V> compositor, ProjectionCollector.Provider<V, P> collectorProvider) {
 		super( builder.scope );
 		this.absoluteFieldPath = builder.objectField.absolutePath();
 		this.absoluteFieldPathComponents = builder.objectField.absolutePathComponents();
-		this.requiredContextAbsoluteFieldPath = accumulatorProvider.isSingleValued()
+		this.requiredContextAbsoluteFieldPath = collectorProvider.isSingleValued()
 				? builder.objectField.closestMultiValuedParentAbsolutePath()
 				: null;
 		this.inners = inners;
 		this.compositor = compositor;
-		this.accumulatorProvider = accumulatorProvider;
+		this.collectorProvider = collectorProvider;
 	}
 
 	@Override
@@ -57,7 +57,7 @@ public String toString() {
 		return getClass().getSimpleName() + "["
 				+ "inners=" + Arrays.toString( inners )
 				+ ", compositor=" + compositor
-				+ ", accumulatorProvider=" + accumulatorProvider
+				+ ", collectorProvider=" + collectorProvider
 				+ "]";
 	}
 
@@ -76,7 +76,7 @@ public Extractor<?, P> request(JsonObject requestBody, ProjectionRequestContext
 		for ( int i = 0; i < inners.length; i++ ) {
 			innerExtractors[i] = inners[i].request( requestBody, innerContext );
 		}
-		return new ObjectFieldExtractor<>( extractorFieldPathComponents, accumulatorProvider.get(), innerExtractors );
+		return new ObjectFieldExtractor<>( extractorFieldPathComponents, collectorProvider.get(), innerExtractors );
 	}
 
 	/**
@@ -85,9 +85,9 @@ public Extractor<?, P> request(JsonObject requestBody, ProjectionRequestContext
 	private class ObjectFieldExtractor<A> extends AccumulatingSourceExtractor<E, V, A, P> {
 		private final Extractor<?, ?>[] inners;
 
-		private ObjectFieldExtractor(String[] fieldPathComponents, ProjectionAccumulator<E, V, A, P> accumulator,
+		private ObjectFieldExtractor(String[] fieldPathComponents, ProjectionCollector<E, V, A, P> collector,
 				Extractor<?, ?>[] inners) {
-			super( fieldPathComponents, accumulator );
+			super( fieldPathComponents, collector );
 			this.inners = inners;
 		}
 
@@ -96,7 +96,7 @@ public String toString() {
 			return getClass().getSimpleName() + "["
 					+ "inners=" + Arrays.toString( inners )
 					+ ", compositor=" + compositor
-					+ ", accumulator=" + accumulator
+					+ ", collector=" + collector
 					+ "]";
 		}
 
@@ -123,8 +123,8 @@ protected boolean canDecodeArrays() {
 		@Override
 		public final P transform(LoadingResult<?> loadingResult, A accumulated,
 				ProjectionTransformContext context) {
-			for ( int i = 0; i < accumulator.size( accumulated ); i++ ) {
-				E transformedData = accumulator.get( accumulated, i );
+			for ( int i = 0; i < collector.size( accumulated ); i++ ) {
+				E transformedData = collector.get( accumulated, i );
 				if ( transformedData == null ) {
 					continue;
 				}
@@ -136,9 +136,9 @@ public final P transform(LoadingResult<?> loadingResult, A accumulated,
 					transformedData = compositor.set( transformedData, j, transformedDataForInner );
 				}
 
-				accumulated = accumulator.transform( accumulated, i, compositor.finish( transformedData ) );
+				accumulated = collector.transform( accumulated, i, compositor.finish( transformedData ) );
 			}
-			return accumulator.finish( accumulated );
+			return collector.finish( accumulated );
 		}
 	}
 
@@ -163,8 +163,8 @@ static class Builder implements CompositeProjectionBuilder {
 
 		@Override
 		public <E, V, P> SearchProjection<P> build(SearchProjection<?>[] inners, ProjectionCompositor<E, V> compositor,
-				ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
-			if ( accumulatorProvider.isSingleValued() && objectField.multiValued() ) {
+				ProjectionCollector.Provider<V, P> collectorProvider) {
+			if ( collectorProvider.isSingleValued() && objectField.multiValued() ) {
 				throw log.invalidSingleValuedProjectionOnMultiValuedField( objectField.absolutePath(),
 						objectField.eventContext() );
 			}
@@ -174,7 +174,7 @@ public <E, V, P> SearchProjection<P> build(SearchProjection<?>[] inners, Project
 				typedInners[i] = ElasticsearchSearchProjection.from( scope, inners[i] );
 			}
 			return new ElasticsearchObjectProjection<>( this, typedInners,
-					compositor, accumulatorProvider );
+					compositor, collectorProvider );
 		}
 	}
 }
diff --git a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ProjectionRequestRootContext.java b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ProjectionRequestRootContext.java
index 01db0cb817a..e0b82dc52bb 100644
--- a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ProjectionRequestRootContext.java
+++ b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/projection/impl/ProjectionRequestRootContext.java
@@ -6,7 +6,7 @@
 
 import org.hibernate.search.backend.elasticsearch.lowlevel.syntax.search.impl.ElasticsearchSearchSyntax;
 import org.hibernate.search.backend.elasticsearch.search.highlighter.impl.ElasticsearchSearchHighlighter;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.spatial.GeoPoint;
 
 public interface ProjectionRequestRootContext extends ProjectionRequestContext {
@@ -19,5 +19,5 @@ public interface ProjectionRequestRootContext extends ProjectionRequestContext {
 
 	ElasticsearchSearchHighlighter queryHighlighter();
 
-	boolean isCompatibleHighlighter(String highlighterName, ProjectionAccumulator.Provider<?, ?> accumulatorProvider);
+	boolean isCompatibleHighlighter(String highlighterName, ProjectionCollector.Provider<?, ?> collectorProvider);
 }
diff --git a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/query/dsl/impl/ElasticsearchSearchQuerySelectStepImpl.java b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/query/dsl/impl/ElasticsearchSearchQuerySelectStepImpl.java
index ae875675f1a..af452ffb0d2 100644
--- a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/query/dsl/impl/ElasticsearchSearchQuerySelectStepImpl.java
+++ b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/query/dsl/impl/ElasticsearchSearchQuerySelectStepImpl.java
@@ -20,9 +20,9 @@
 import org.hibernate.search.engine.search.predicate.SearchPredicate;
 import org.hibernate.search.engine.search.predicate.dsl.PredicateFinalStep;
 import org.hibernate.search.engine.search.predicate.dsl.SimpleBooleanPredicateClausesCollector;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.dsl.ProjectionFinalStep;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionCompositor;
 import org.hibernate.search.engine.search.query.dsl.spi.AbstractSearchQuerySelectStep;
 import org.hibernate.search.engine.search.query.spi.SearchQueryIndexScope;
@@ -83,7 +83,7 @@ public <P> ElasticsearchSearchQueryWhereStep<P, LOS> select(SearchProjection<P>
 	public ElasticsearchSearchQueryWhereStep<List<?>, LOS> select(SearchProjection<?>... projections) {
 		return select( scope.projectionBuilders().composite()
 				.build( projections, ProjectionCompositor.fromList( projections.length ),
-						ProjectionAccumulator.single() ) );
+						ProjectionCollector.nullable() ) );
 	}
 
 	@Override
diff --git a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/query/impl/ElasticsearchSearchQueryRequestContext.java b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/query/impl/ElasticsearchSearchQueryRequestContext.java
index 9da2e5fa0c9..80a2efb6e90 100644
--- a/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/query/impl/ElasticsearchSearchQueryRequestContext.java
+++ b/backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/query/impl/ElasticsearchSearchQueryRequestContext.java
@@ -23,7 +23,7 @@
 import org.hibernate.search.engine.search.common.NamedValues;
 import org.hibernate.search.engine.search.common.spi.SearchQueryElementTypeKey;
 import org.hibernate.search.engine.search.loading.spi.SearchLoadingContext;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.query.spi.QueryParameters;
 import org.hibernate.search.engine.spatial.GeoPoint;
 import org.hibernate.search.util.common.logging.impl.LoggerFactory;
@@ -144,17 +144,17 @@ public ElasticsearchSearchHighlighter queryHighlighter() {
 	}
 
 	@Override
-	public boolean isCompatibleHighlighter(String highlighterName, ProjectionAccumulator.Provider<?, ?> accumulatorProvider) {
+	public boolean isCompatibleHighlighter(String highlighterName, ProjectionCollector.Provider<?, ?> collectorProvider) {
 		ElasticsearchSearchHighlighter highlighter = highlighter( highlighterName );
 		if ( ElasticsearchSearchHighlighterImpl.NO_OPTIONS_CONFIGURATION == highlighter ) {
 			// if there was no highlighter configured at all it means that the settings are default,
-			// and we assume that they are incompatible with the single-valued accumulator:
+			// and we assume that they are incompatible with the single-valued collector:
 			return queryHighlighter != null
-					? queryHighlighter.isCompatible( accumulatorProvider )
-					: !accumulatorProvider.isSingleValued();
+					? queryHighlighter.isCompatible( collectorProvider )
+					: !collectorProvider.isSingleValued();
 		}
 		else {
-			return highlighter.isCompatible( accumulatorProvider );
+			return highlighter.isCompatible( collectorProvider );
 		}
 	}
 
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/logging/impl/Log.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/logging/impl/Log.java
index f4d827d44c1..7473ee29b58 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/logging/impl/Log.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/logging/impl/Log.java
@@ -537,7 +537,7 @@ SearchException invalidFieldValueType(@FormatWith(ClassFormatter.class) Class<?>
 	@Message(id = ID_OFFSET + 131,
 			value = "Invalid cardinality for projection on field '%1$s': the projection is single-valued,"
 					+ " but this field is multi-valued."
-					+ " Make sure to call '.multi()' when you create the projection.")
+					+ " Make sure to call '.collector(...)' when you create the projection.")
 	SearchException invalidSingleValuedProjectionOnMultiValuedField(String absolutePath, @Param EventContext context);
 
 	@Message(id = ID_OFFSET + 135,
@@ -600,9 +600,9 @@ SearchException invalidContextForProjectionOnField(String absolutePath,
 			value = "Invalid cardinality for projection on field '%1$s': the projection is single-valued,"
 					+ " but this field is effectively multi-valued in this context,"
 					+ " because parent object field '%2$s' is multi-valued."
-					+ " Either call '.multi()' when you create the projection on field '%1$s',"
+					+ " Either call '.collector(...)' when you create the projection on field '%1$s',"
 					+ " or wrap that projection in an object projection like this:"
-					+ " 'f.object(\"%2$s\").from(<the projection on field %1$s>).as(...).multi()'.")
+					+ " 'f.object(\"%2$s\").from(<the projection on field %1$s>).as(...).collector(...)'.")
 	SearchException invalidSingleValuedProjectionOnValueFieldInMultiValuedObjectField(String absolutePath,
 			String objectFieldAbsolutePath);
 
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LuceneAbstractSearchHighlighter.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LuceneAbstractSearchHighlighter.java
index 956a225ac83..a9bbaa0332c 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LuceneAbstractSearchHighlighter.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LuceneAbstractSearchHighlighter.java
@@ -26,7 +26,7 @@
 import org.hibernate.search.engine.search.highlighter.spi.BoundaryScannerType;
 import org.hibernate.search.engine.search.highlighter.spi.SearchHighlighterBuilder;
 import org.hibernate.search.engine.search.highlighter.spi.SearchHighlighterType;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.util.common.impl.Contracts;
 import org.hibernate.search.util.common.logging.impl.LoggerFactory;
 
@@ -193,9 +193,9 @@ public Set<String> indexNames() {
 
 	public abstract <A, T> Values<A> createValues(String parentDocumentPath, String nestedDocumentPath,
 			String absoluteFieldPath, Analyzer analyzer, ProjectionExtractContext context,
-			ProjectionAccumulator<String, ?, A, T> accumulator);
+			ProjectionCollector<String, ?, A, T> collector);
 
-	public boolean isCompatible(ProjectionAccumulator.Provider<?, ?> provider) {
+	public boolean isCompatible(ProjectionCollector.Provider<?, ?> provider) {
 		return !provider.isSingleValued()
 				|| ( provider.isSingleValued() && ( numberOfFragments != null && numberOfFragments.equals( 1 ) ) );
 	}
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LuceneFastVectorSearchHighlighter.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LuceneFastVectorSearchHighlighter.java
index a2669d61aab..d425c33fc87 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LuceneFastVectorSearchHighlighter.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LuceneFastVectorSearchHighlighter.java
@@ -20,7 +20,7 @@
 import org.hibernate.search.engine.search.highlighter.dsl.HighlighterFragmenter;
 import org.hibernate.search.engine.search.highlighter.spi.BoundaryScannerType;
 import org.hibernate.search.engine.search.highlighter.spi.SearchHighlighterType;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.document.Field;
@@ -86,9 +86,10 @@ public LuceneAbstractSearchHighlighter withFallbackDefaults() {
 	@Override
 	public <A, T> Values<A> createValues(String parentDocumentPath, String nestedDocumentPath,
 			String absoluteFieldPath, Analyzer analyzer, ProjectionExtractContext context,
-			ProjectionAccumulator<String, ?, A, T> accumulator) {
+			ProjectionCollector<String, ?, A, T> collector) {
 		return new FastVectorHighlighterValues<>( parentDocumentPath, nestedDocumentPath, absoluteFieldPath, context,
-				accumulator );
+				collector
+		);
 	}
 
 	@Override
@@ -108,8 +109,8 @@ private final class FastVectorHighlighterValues<A, T> extends HighlighterValues<
 		private final Integer maxNumFragments;
 
 		FastVectorHighlighterValues(String parentDocumentPath, String nestedDocumentPath, String field,
-				ProjectionExtractContext context, ProjectionAccumulator<String, ?, A, T> accumulator) {
-			super( parentDocumentPath, nestedDocumentPath, context.collectorExecutionContext(), accumulator );
+				ProjectionExtractContext context, ProjectionCollector<String, ?, A, T> collector) {
+			super( parentDocumentPath, nestedDocumentPath, context.collectorExecutionContext(), collector );
 			this.field = field;
 
 			this.highlighter = new FastVectorHighlighter();
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LucenePlainSearchHighlighter.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LucenePlainSearchHighlighter.java
index 6ab573d2898..6596291e568 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LucenePlainSearchHighlighter.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LucenePlainSearchHighlighter.java
@@ -21,7 +21,7 @@
 import org.hibernate.search.engine.search.highlighter.dsl.HighlighterFragmenter;
 import org.hibernate.search.engine.search.highlighter.spi.BoundaryScannerType;
 import org.hibernate.search.engine.search.highlighter.spi.SearchHighlighterType;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.index.IndexableField;
@@ -87,9 +87,9 @@ public LuceneAbstractSearchHighlighter withFallbackDefaults() {
 	@Override
 	public <A, T> Values<A> createValues(String parentDocumentPath, String nestedDocumentPath,
 			String absoluteFieldPath, Analyzer analyzer, ProjectionExtractContext context,
-			ProjectionAccumulator<String, ?, A, T> accumulator) {
+			ProjectionCollector<String, ?, A, T> collector) {
 		return new PlainHighlighterValues<>(
-				parentDocumentPath, nestedDocumentPath, absoluteFieldPath, analyzer, context, accumulator );
+				parentDocumentPath, nestedDocumentPath, absoluteFieldPath, analyzer, context, collector );
 	}
 
 	@Override
@@ -109,8 +109,8 @@ private final class PlainHighlighterValues<A, T> extends HighlighterValues<A, T>
 		private final String field;
 
 		PlainHighlighterValues(String parentDocumentPath, String nestedDocumentPath, String field, Analyzer analyzer,
-				ProjectionExtractContext context, ProjectionAccumulator<String, ?, A, T> accumulator) {
-			super( parentDocumentPath, nestedDocumentPath, context.collectorExecutionContext(), accumulator );
+				ProjectionExtractContext context, ProjectionCollector<String, ?, A, T> collector) {
+			super( parentDocumentPath, nestedDocumentPath, context.collectorExecutionContext(), collector );
 			this.storedFieldsValuesDelegate = context.collectorExecutionContext().storedFieldsValuesDelegate();
 			this.field = field;
 			this.analyzer = analyzer;
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LuceneUnifiedSearchHighlighter.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LuceneUnifiedSearchHighlighter.java
index 969145187ad..385f2d563a4 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LuceneUnifiedSearchHighlighter.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/highlighter/impl/LuceneUnifiedSearchHighlighter.java
@@ -21,7 +21,7 @@
 import org.hibernate.search.engine.search.highlighter.dsl.HighlighterFragmenter;
 import org.hibernate.search.engine.search.highlighter.spi.BoundaryScannerType;
 import org.hibernate.search.engine.search.highlighter.spi.SearchHighlighterType;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.search.IndexSearcher;
@@ -90,9 +90,9 @@ public LuceneAbstractSearchHighlighter withFallbackDefaults() {
 	@Override
 	public <A, T> Values<A> createValues(String parentDocumentPath, String nestedDocumentPath,
 			String absoluteFieldPath, Analyzer analyzer, ProjectionExtractContext context,
-			ProjectionAccumulator<String, ?, A, T> accumulator) {
+			ProjectionCollector<String, ?, A, T> collector) {
 		return new UnifiedHighlighterValues<>(
-				parentDocumentPath, nestedDocumentPath, absoluteFieldPath, analyzer, context, accumulator );
+				parentDocumentPath, nestedDocumentPath, absoluteFieldPath, analyzer, context, collector );
 	}
 
 	@Override
@@ -109,8 +109,8 @@ private final class UnifiedHighlighterValues<A, T> extends HighlighterValues<A,
 		private final MultiValueUnifiedHighlighter highlighter;
 
 		UnifiedHighlighterValues(String parentDocumentPath, String nestedDocumentPath, String field, Analyzer analyzer,
-				ProjectionExtractContext context, ProjectionAccumulator<String, ?, A, T> accumulator) {
-			super( parentDocumentPath, nestedDocumentPath, context.collectorExecutionContext(), accumulator );
+				ProjectionExtractContext context, ProjectionCollector<String, ?, A, T> collector) {
+			super( parentDocumentPath, nestedDocumentPath, context.collectorExecutionContext(), collector );
 			this.fieldsIn = new String[] { field };
 			this.maxPassagesIn = new int[] { LuceneUnifiedSearchHighlighter.this.numberOfFragments };
 			this.query = context.collectorExecutionContext().originalQuery();
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/AbstractNestingAwareAccumulatingValues.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/AbstractNestingAwareAccumulatingValues.java
index cc564d49720..c5cb96b82dc 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/AbstractNestingAwareAccumulatingValues.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/AbstractNestingAwareAccumulatingValues.java
@@ -10,23 +10,23 @@
 import org.hibernate.search.backend.lucene.lowlevel.collector.impl.Values;
 import org.hibernate.search.backend.lucene.lowlevel.join.impl.ChildDocIds;
 import org.hibernate.search.backend.lucene.lowlevel.join.impl.NestedDocsProvider;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.search.DocIdSetIterator;
 
 abstract class AbstractNestingAwareAccumulatingValues<E, A> implements Values<A> {
 	private final NestedDocsProvider nestedDocsProvider;
-	protected final ProjectionAccumulator<E, ?, A, ?> accumulator;
+	protected final ProjectionCollector<E, ?, A, ?> collector;
 
 	protected ChildDocIds currentLeafChildDocIds;
 
 	AbstractNestingAwareAccumulatingValues(String parentDocumentPath, String nestedDocumentPath,
-			ProjectionAccumulator<E, ?, A, ?> accumulator, TopDocsDataCollectorExecutionContext context) {
+			ProjectionCollector<E, ?, A, ?> collector, TopDocsDataCollectorExecutionContext context) {
 		this.nestedDocsProvider = nestedDocumentPath == null || nestedDocumentPath.equals( parentDocumentPath )
 				? null
 				: context.createNestedDocsProvider( parentDocumentPath, nestedDocumentPath );
-		this.accumulator = accumulator;
+		this.collector = collector;
 	}
 
 	@Override
@@ -44,7 +44,7 @@ protected DocIdSetIterator doContext(LeafReaderContext context) throws IOExcepti
 
 	@Override
 	public final A get(int parentDocId) throws IOException {
-		A accumulated = accumulator.createInitial();
+		A accumulated = collector.createInitial();
 
 		if ( nestedDocsProvider == null ) {
 			// No nesting: we work directly on the parent doc.
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneCompositeProjection.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneCompositeProjection.java
index 36d41b6c76f..c61fd1c8803 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneCompositeProjection.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneCompositeProjection.java
@@ -10,9 +10,9 @@
 import org.hibernate.search.backend.lucene.lowlevel.collector.impl.Values;
 import org.hibernate.search.backend.lucene.search.common.impl.LuceneSearchIndexScope;
 import org.hibernate.search.engine.search.loading.spi.LoadingResult;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.spi.CompositeProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionCompositor;
 
 import org.apache.lucene.index.LeafReaderContext;
@@ -32,14 +32,14 @@ class LuceneCompositeProjection<E, V, A, P>
 
 	private final LuceneSearchProjection<?>[] inners;
 	private final ProjectionCompositor<E, V> compositor;
-	private final ProjectionAccumulator<E, V, A, P> accumulator;
+	private final ProjectionCollector<E, V, A, P> collector;
 
 	public LuceneCompositeProjection(Builder builder, LuceneSearchProjection<?>[] inners,
-			ProjectionCompositor<E, V> compositor, ProjectionAccumulator<E, V, A, P> accumulator) {
+			ProjectionCompositor<E, V> compositor, ProjectionCollector<E, V, A, P> collector) {
 		super( builder.scope );
 		this.inners = inners;
 		this.compositor = compositor;
-		this.accumulator = accumulator;
+		this.collector = collector;
 	}
 
 	@Override
@@ -47,7 +47,7 @@ public String toString() {
 		return getClass().getSimpleName() + "["
 				+ "inners=" + Arrays.toString( inners )
 				+ ", compositor=" + compositor
-				+ ", accumulator=" + accumulator
+				+ ", collector=" + collector
 				+ "]";
 	}
 
@@ -72,7 +72,7 @@ public String toString() {
 			return getClass().getSimpleName() + "["
 					+ "inners=" + Arrays.toString( inners )
 					+ ", compositor=" + compositor
-					+ ", accumulator=" + accumulator
+					+ ", collector=" + collector
 					+ "]";
 		}
 
@@ -101,14 +101,14 @@ public void context(LeafReaderContext context) throws IOException {
 
 			@Override
 			public A get(int doc) throws IOException {
-				A accumulated = accumulator.createInitial();
+				A accumulated = collector.createInitial();
 
 				E components = compositor.createInitial();
 				for ( int i = 0; i < inners.length; i++ ) {
 					Object extractedDataForInner = inners[i].get( doc );
 					components = compositor.set( components, i, extractedDataForInner );
 				}
-				accumulated = accumulator.accumulate( accumulated, components );
+				accumulated = collector.accumulate( accumulated, components );
 
 				return accumulated;
 			}
@@ -117,8 +117,8 @@ public A get(int doc) throws IOException {
 		@Override
 		public final P transform(LoadingResult<?> loadingResult, A accumulated,
 				ProjectionTransformContext context) {
-			for ( int i = 0; i < accumulator.size( accumulated ); i++ ) {
-				E transformedData = accumulator.get( accumulated, i );
+			for ( int i = 0; i < collector.size( accumulated ); i++ ) {
+				E transformedData = collector.get( accumulated, i );
 				// Transform in-place
 				for ( int j = 0; j < inners.length; j++ ) {
 					Object extractedDataForInner = compositor.get( transformedData, j );
@@ -126,9 +126,9 @@ public final P transform(LoadingResult<?> loadingResult, A accumulated,
 							extractedDataForInner, context );
 					transformedData = compositor.set( transformedData, j, transformedDataForInner );
 				}
-				accumulated = accumulator.transform( accumulated, i, compositor.finish( transformedData ) );
+				accumulated = collector.transform( accumulated, i, compositor.finish( transformedData ) );
 			}
-			return accumulator.finish( accumulated );
+			return collector.finish( accumulated );
 		}
 	}
 
@@ -142,14 +142,14 @@ static class Builder implements CompositeProjectionBuilder {
 
 		@Override
 		public <E, V, P> SearchProjection<P> build(SearchProjection<?>[] inners, ProjectionCompositor<E, V> compositor,
-				ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
+				ProjectionCollector.Provider<V, P> collectorProvider) {
 			LuceneSearchProjection<?>[] typedInners =
 					new LuceneSearchProjection<?>[inners.length];
 			for ( int i = 0; i < inners.length; i++ ) {
 				typedInners[i] = LuceneSearchProjection.from( scope, inners[i] );
 			}
 			return new LuceneCompositeProjection<>( this, typedInners,
-					compositor, accumulatorProvider.get() );
+					compositor, collectorProvider.get() );
 		}
 	}
 }
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneDistanceToFieldProjection.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneDistanceToFieldProjection.java
index 7a4f2bfbebe..5ffad286d11 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneDistanceToFieldProjection.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneDistanceToFieldProjection.java
@@ -17,9 +17,9 @@
 import org.hibernate.search.backend.lucene.types.codec.impl.LuceneFieldCodec;
 import org.hibernate.search.engine.backend.types.converter.spi.ProjectionConverter;
 import org.hibernate.search.engine.search.loading.spi.LoadingResult;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.spi.DistanceToFieldProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.spatial.DistanceUnit;
 import org.hibernate.search.engine.spatial.GeoPoint;
 import org.hibernate.search.util.common.logging.impl.LoggerFactory;
@@ -49,27 +49,27 @@ public class LuceneDistanceToFieldProjection<P> extends AbstractLuceneProjection
 	private final GeoPoint center;
 	private final DistanceUnit unit;
 
-	private final ProjectionAccumulator.Provider<Double, P> accumulatorProvider;
+	private final ProjectionCollector.Provider<Double, P> collectorProvider;
 
 	private final LuceneFieldProjection<Double, Double, P, ?> fieldProjection;
 
 	private LuceneDistanceToFieldProjection(Builder builder,
-			ProjectionAccumulator.Provider<Double, P> accumulatorProvider) {
+			ProjectionCollector.Provider<Double, P> collectorProvider) {
 		super( builder );
 		this.absoluteFieldPath = builder.field.absolutePath();
 		this.nestedDocumentPath = builder.field.nestedDocumentPath();
-		this.requiredContextAbsoluteFieldPath = accumulatorProvider.isSingleValued()
+		this.requiredContextAbsoluteFieldPath = collectorProvider.isSingleValued()
 				? builder.field.closestMultiValuedParentAbsolutePath()
 				: null;
 		this.codec = builder.codec;
 		this.center = builder.center;
 		this.unit = builder.unit;
-		this.accumulatorProvider = accumulatorProvider;
+		this.collectorProvider = collectorProvider;
 		if ( builder.field.multiValued() ) {
 			// For multi-valued fields, use a field projection, because we need order to be preserved.
 			this.fieldProjection = new LuceneFieldProjection<>(
 					builder.scope, builder.field,
-					this::computeDistanceWithUnit, NO_OP_DOUBLE_CONVERTER, accumulatorProvider
+					this::computeDistanceWithUnit, NO_OP_DOUBLE_CONVERTER, collectorProvider
 			);
 		}
 		else {
@@ -83,7 +83,7 @@ public String toString() {
 		return getClass().getSimpleName() + "["
 				+ "absoluteFieldPath=" + absoluteFieldPath
 				+ ", center=" + center
-				+ ", accumulatorProvider=" + accumulatorProvider
+				+ ", collectorProvider=" + collectorProvider
 				+ "]";
 	}
 
@@ -99,7 +99,7 @@ public Extractor<?, P> request(ProjectionRequestContext context) {
 				throw log.invalidSingleValuedProjectionOnValueFieldInMultiValuedObjectField(
 						absoluteFieldPath, requiredContextAbsoluteFieldPath );
 			}
-			return new DocValuesBasedDistanceExtractor<>( accumulatorProvider.get(),
+			return new DocValuesBasedDistanceExtractor<>( collectorProvider.get(),
 					context.absoluteCurrentNestedFieldPath() );
 		}
 	}
@@ -108,12 +108,12 @@ public Extractor<?, P> request(ProjectionRequestContext context) {
 	 * @param <A> The type of the temporary storage for accumulated values, before and after being transformed.
 	 */
 	private class DocValuesBasedDistanceExtractor<A> implements Extractor<A, P> {
-		private final ProjectionAccumulator<Double, Double, A, P> accumulator;
+		private final ProjectionCollector<Double, Double, A, P> collector;
 		private final String contextAbsoluteFieldPath;
 
-		private DocValuesBasedDistanceExtractor(ProjectionAccumulator<Double, Double, A, P> accumulator,
+		private DocValuesBasedDistanceExtractor(ProjectionCollector<Double, Double, A, P> collector,
 				String contextAbsoluteFieldPath) {
-			this.accumulator = accumulator;
+			this.collector = collector;
 			this.contextAbsoluteFieldPath = contextAbsoluteFieldPath;
 		}
 
@@ -122,7 +122,7 @@ public String toString() {
 			return getClass().getSimpleName() + "["
 					+ "absoluteFieldPath=" + absoluteFieldPath
 					+ ", center=" + center
-					+ ", accumulator=" + accumulator
+					+ ", collector=" + collector
 					+ "]";
 		}
 
@@ -140,7 +140,7 @@ private class DocValuesBasedDistanceValues
 
 			public DocValuesBasedDistanceValues(TopDocsDataCollectorExecutionContext context) {
 				super( contextAbsoluteFieldPath, nestedDocumentPath,
-						DocValuesBasedDistanceExtractor.this.accumulator, context );
+						DocValuesBasedDistanceExtractor.this.collector, context );
 			}
 
 			@Override
@@ -155,7 +155,7 @@ protected A accumulate(A accumulated, int docId) throws IOException {
 				if ( currentLeafValues.advanceExact( docId ) ) {
 					for ( int i = 0; i < currentLeafValues.docValueCount(); i++ ) {
 						Double distanceOrNull = currentLeafValues.nextValue();
-						accumulated = accumulator.accumulate( accumulated, unit.fromMeters( distanceOrNull ) );
+						accumulated = collector.accumulate( accumulated, unit.fromMeters( distanceOrNull ) );
 					}
 				}
 				return accumulated;
@@ -166,7 +166,7 @@ protected A accumulate(A accumulated, int docId) throws IOException {
 		public P transform(LoadingResult<?> loadingResult, A extractedData,
 				ProjectionTransformContext context) {
 			// Nothing to transform: we take the values as they are.
-			return accumulator.finish( extractedData );
+			return collector.finish( extractedData );
 		}
 	}
 
@@ -229,11 +229,11 @@ public void unit(DistanceUnit unit) {
 		}
 
 		@Override
-		public <P> SearchProjection<P> build(ProjectionAccumulator.Provider<Double, P> accumulatorProvider) {
-			if ( accumulatorProvider.isSingleValued() && field.multiValued() ) {
+		public <P> SearchProjection<P> build(ProjectionCollector.Provider<Double, P> collectorProvider) {
+			if ( collectorProvider.isSingleValued() && field.multiValued() ) {
 				throw log.invalidSingleValuedProjectionOnMultiValuedField( field.absolutePath(), field.eventContext() );
 			}
-			return new LuceneDistanceToFieldProjection<>( this, accumulatorProvider );
+			return new LuceneDistanceToFieldProjection<>( this, collectorProvider );
 		}
 	}
 }
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneFieldHighlightProjection.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneFieldHighlightProjection.java
index 8c0cd0ebc2b..cf753c3e500 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneFieldHighlightProjection.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneFieldHighlightProjection.java
@@ -17,9 +17,9 @@
 import org.hibernate.search.backend.lucene.search.highlighter.impl.LuceneAbstractSearchHighlighter;
 import org.hibernate.search.engine.reporting.spi.EventContexts;
 import org.hibernate.search.engine.search.loading.spi.LoadingResult;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.dsl.spi.HighlightProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.index.LeafReaderContext;
@@ -32,22 +32,22 @@ public class LuceneFieldHighlightProjection<T> implements LuceneSearchProjection
 	private final String highlighterName;
 	private final String nestedDocumentPath;
 	private final LuceneSearchIndexValueFieldTypeContext<?> typeContext;
-	private final ProjectionAccumulator.Provider<String, T> accumulatorProvider;
+	private final ProjectionCollector.Provider<String, T> collectorProvider;
 
-	private LuceneFieldHighlightProjection(Builder builder, ProjectionAccumulator.Provider<String, T> accumulatorProvider) {
-		this( builder.scope, builder.field, builder.highlighterName(), accumulatorProvider );
+	private LuceneFieldHighlightProjection(Builder builder, ProjectionCollector.Provider<String, T> collectorProvider) {
+		this( builder.scope, builder.field, builder.highlighterName(), collectorProvider );
 	}
 
 	LuceneFieldHighlightProjection(LuceneSearchIndexScope<?> scope,
 			LuceneSearchIndexValueFieldContext<?> field,
-			String highlighterName, ProjectionAccumulator.Provider<String, T> accumulatorProvider) {
+			String highlighterName, ProjectionCollector.Provider<String, T> collectorProvider) {
 		this.indexNames = scope.hibernateSearchIndexNames();
 		this.analyzer = field.type().searchAnalyzerOrNormalizer();
 		this.absoluteFieldPath = field.absolutePath();
 		this.highlighterName = highlighterName;
 		this.nestedDocumentPath = field.nestedDocumentPath();
 		this.typeContext = field.type();
-		this.accumulatorProvider = accumulatorProvider;
+		this.collectorProvider = collectorProvider;
 	}
 
 	@Override
@@ -77,12 +77,12 @@ public Extractor<?, T> request(ProjectionRequestContext context) {
 			throw log.highlighterTypeNotSupported( highlighter.type(), absoluteFieldPath );
 		}
 		highlighter.request( context, absoluteFieldPath );
-		if ( !highlighter.isCompatible( accumulatorProvider ) ) {
+		if ( !highlighter.isCompatible( collectorProvider ) ) {
 			throw log.highlighterIncompatibleCardinality();
 		}
 
 		return new FieldHighlightExtractor<>( context.absoluteCurrentNestedFieldPath(), highlighter,
-				accumulatorProvider.get()
+				collectorProvider.get()
 		);
 	}
 
@@ -90,13 +90,13 @@ public Extractor<?, T> request(ProjectionRequestContext context) {
 	private class FieldHighlightExtractor<A> implements Extractor<A, T> {
 		private final String parentDocumentPath;
 		private final LuceneAbstractSearchHighlighter highlighter;
-		private final ProjectionAccumulator<String, String, A, T> accumulator;
+		private final ProjectionCollector<String, String, A, T> collector;
 
 		private FieldHighlightExtractor(String parentDocumentPath, LuceneAbstractSearchHighlighter highlighter,
-				ProjectionAccumulator<String, String, A, T> accumulator) {
+				ProjectionCollector<String, String, A, T> collector) {
 			this.parentDocumentPath = parentDocumentPath;
 			this.highlighter = highlighter;
-			this.accumulator = accumulator;
+			this.collector = collector;
 		}
 
 		@Override
@@ -107,14 +107,14 @@ public Values<A> values(ProjectionExtractContext context) {
 					absoluteFieldPath,
 					analyzer,
 					context,
-					accumulator
+					collector
 			);
 		}
 
 		@Override
 		public T transform(LoadingResult<?> loadingResult, A extractedData,
 				ProjectionTransformContext context) {
-			return accumulator.finish( extractedData );
+			return collector.finish( extractedData );
 		}
 	}
 
@@ -124,8 +124,8 @@ public abstract static class HighlighterValues<A, T> extends AbstractNestingAwar
 
 		protected HighlighterValues(String parentDocumentPath, String nestedDocumentPath,
 				TopDocsDataCollectorExecutionContext context,
-				ProjectionAccumulator<String, ?, A, T> accumulator) {
-			super( parentDocumentPath, nestedDocumentPath, accumulator, context );
+				ProjectionCollector<String, ?, A, T> collector) {
+			super( parentDocumentPath, nestedDocumentPath, collector, context );
 		}
 
 		@Override
@@ -139,7 +139,7 @@ public void context(LeafReaderContext context) throws IOException {
 
 		@Override
 		protected A accumulate(A accumulated, int docId) throws IOException {
-			return accumulator.accumulateAll( accumulated, highlight( docId ) );
+			return collector.accumulateAll( accumulated, highlight( docId ) );
 		}
 
 		protected abstract List<String> highlight(int doc) throws IOException;
@@ -175,8 +175,8 @@ protected String highlighterName() {
 		}
 
 		@Override
-		public <V> SearchProjection<V> build(ProjectionAccumulator.Provider<String, V> accumulatorProvider) {
-			return new LuceneFieldHighlightProjection<>( this, accumulatorProvider );
+		public <V> SearchProjection<V> build(ProjectionCollector.Provider<String, V> collectorProvider) {
+			return new LuceneFieldHighlightProjection<>( this, collectorProvider );
 		}
 	}
 }
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneFieldProjection.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneFieldProjection.java
index 582cbc3c2f2..541a5522055 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneFieldProjection.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneFieldProjection.java
@@ -19,9 +19,9 @@
 import org.hibernate.search.engine.backend.types.converter.spi.ProjectionConverter;
 import org.hibernate.search.engine.search.common.ValueModel;
 import org.hibernate.search.engine.search.loading.spi.LoadingResult;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.spi.FieldProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.util.common.logging.impl.LoggerFactory;
 
 import org.apache.lucene.document.Document;
@@ -44,33 +44,33 @@ public class LuceneFieldProjection<F, V, P, T> extends AbstractLuceneProjection<
 
 	private final Function<IndexableField, T> decodeFunction;
 	private final ProjectionConverter<T, ? extends V> converter;
-	private final ProjectionAccumulator.Provider<V, P> accumulatorProvider;
+	private final ProjectionCollector.Provider<V, P> collectorProvider;
 
-	private LuceneFieldProjection(Builder<F, V, T> builder, ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
-		this( builder.scope, builder.field, builder.decodeFunction, builder.converter, accumulatorProvider );
+	private LuceneFieldProjection(Builder<F, V, T> builder, ProjectionCollector.Provider<V, P> collectorProvider) {
+		this( builder.scope, builder.field, builder.decodeFunction, builder.converter, collectorProvider );
 	}
 
 	LuceneFieldProjection(LuceneSearchIndexScope<?> scope,
 			LuceneSearchIndexValueFieldContext<?> field,
 			Function<IndexableField, T> decodeFunction,
 			ProjectionConverter<T, ? extends V> converter,
-			ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
+			ProjectionCollector.Provider<V, P> collectorProvider) {
 		super( scope );
 		this.absoluteFieldPath = field.absolutePath();
 		this.nestedDocumentPath = field.nestedDocumentPath();
-		this.requiredContextAbsoluteFieldPath = accumulatorProvider.isSingleValued()
+		this.requiredContextAbsoluteFieldPath = collectorProvider.isSingleValued()
 				? field.closestMultiValuedParentAbsolutePath()
 				: null;
 		this.decodeFunction = decodeFunction;
 		this.converter = converter;
-		this.accumulatorProvider = accumulatorProvider;
+		this.collectorProvider = collectorProvider;
 	}
 
 	@Override
 	public String toString() {
 		return getClass().getSimpleName() + "["
 				+ "absoluteFieldPath=" + absoluteFieldPath
-				+ ", accumulatorProvider=" + accumulatorProvider
+				+ ", collectorProvider=" + collectorProvider
 				+ "]";
 	}
 
@@ -83,7 +83,7 @@ public ValueFieldExtractor<?> request(ProjectionRequestContext context) {
 					absoluteFieldPath, requiredContextAbsoluteFieldPath );
 		}
 		context.requireStoredField( absoluteFieldPath, nestedDocumentPath );
-		return new ValueFieldExtractor<>( context.absoluteCurrentNestedFieldPath(), accumulatorProvider.get() );
+		return new ValueFieldExtractor<>( context.absoluteCurrentNestedFieldPath(), collectorProvider.get() );
 	}
 
 	/**
@@ -92,10 +92,10 @@ public ValueFieldExtractor<?> request(ProjectionRequestContext context) {
 	private class ValueFieldExtractor<A> implements LuceneSearchProjection.Extractor<A, P> {
 
 		private final String contextAbsoluteFieldPath;
-		private final ProjectionAccumulator<T, V, A, P> accumulator;
+		private final ProjectionCollector<T, V, A, P> collector;
 
-		public ValueFieldExtractor(String contextAbsoluteFieldPath, ProjectionAccumulator<T, V, A, P> accumulator) {
-			this.accumulator = accumulator;
+		public ValueFieldExtractor(String contextAbsoluteFieldPath, ProjectionCollector<T, V, A, P> collector) {
+			this.collector = collector;
 			this.contextAbsoluteFieldPath = contextAbsoluteFieldPath;
 		}
 
@@ -103,21 +103,21 @@ public ValueFieldExtractor(String contextAbsoluteFieldPath, ProjectionAccumulato
 		public String toString() {
 			return getClass().getSimpleName() + "["
 					+ "absoluteFieldPath=" + absoluteFieldPath
-					+ ", accumulator=" + accumulator
+					+ ", collector=" + collector
 					+ "]";
 		}
 
 		@Override
 		public Values<A> values(ProjectionExtractContext context) {
-			return new StoredFieldValues( accumulator, context.collectorExecutionContext() );
+			return new StoredFieldValues( collector, context.collectorExecutionContext() );
 		}
 
 		private class StoredFieldValues extends AbstractNestingAwareAccumulatingValues<T, A> {
 			private final StoredFieldsValuesDelegate delegate;
 
-			public StoredFieldValues(ProjectionAccumulator<T, V, A, P> accumulator,
+			public StoredFieldValues(ProjectionCollector<T, V, A, P> collector,
 					TopDocsDataCollectorExecutionContext context) {
-				super( contextAbsoluteFieldPath, nestedDocumentPath, accumulator, context );
+				super( contextAbsoluteFieldPath, nestedDocumentPath, collector, context );
 				this.delegate = context.storedFieldsValuesDelegate();
 			}
 
@@ -133,7 +133,7 @@ protected A accumulate(A accumulated, int docId) {
 				for ( IndexableField field : document.getFields() ) {
 					if ( field.name().equals( absoluteFieldPath ) ) {
 						T decoded = decodeFunction.apply( field );
-						accumulated = accumulator.accumulate( accumulated, decoded );
+						accumulated = collector.accumulate( accumulated, decoded );
 					}
 				}
 				return accumulated;
@@ -143,8 +143,8 @@ protected A accumulate(A accumulated, int docId) {
 		@Override
 		public P transform(LoadingResult<?> loadingResult, A extractedData, ProjectionTransformContext context) {
 			FromDocumentValueConvertContext convertContext = context.fromDocumentValueConvertContext();
-			A transformedData = accumulator.transformAll( extractedData, converter, convertContext );
-			return accumulator.finish( transformedData );
+			A transformedData = collector.transformAll( extractedData, converter.delegate(), convertContext );
+			return collector.finish( transformedData );
 		}
 	}
 
@@ -216,11 +216,11 @@ private Builder(LuceneSearchIndexScope<?> scope, LuceneSearchIndexValueFieldCont
 		}
 
 		@Override
-		public <P> SearchProjection<P> build(ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
-			if ( accumulatorProvider.isSingleValued() && field.multiValued() ) {
+		public <P> SearchProjection<P> build(ProjectionCollector.Provider<V, P> collectorProvider) {
+			if ( collectorProvider.isSingleValued() && field.multiValued() ) {
 				throw log.invalidSingleValuedProjectionOnMultiValuedField( field.absolutePath(), field.eventContext() );
 			}
-			return new LuceneFieldProjection<>( this, accumulatorProvider );
+			return new LuceneFieldProjection<>( this, collectorProvider );
 		}
 	}
 }
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneObjectProjection.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneObjectProjection.java
index 62c748546a9..de1c02b82c2 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneObjectProjection.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/projection/impl/LuceneObjectProjection.java
@@ -16,9 +16,9 @@
 import org.hibernate.search.backend.lucene.search.predicate.impl.PredicateRequestContext;
 import org.hibernate.search.engine.search.loading.spi.LoadingResult;
 import org.hibernate.search.engine.search.predicate.spi.PredicateTypeKeys;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.spi.CompositeProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionCompositor;
 import org.hibernate.search.engine.search.projection.spi.ProjectionTypeKeys;
 import org.hibernate.search.util.common.SearchException;
@@ -47,21 +47,21 @@ public class LuceneObjectProjection<E, V, P>
 	private final String requiredContextAbsoluteFieldPath;
 	private final LuceneSearchProjection<?>[] inners;
 	private final ProjectionCompositor<E, V> compositor;
-	private final ProjectionAccumulator.Provider<V, P> accumulatorProvider;
+	private final ProjectionCollector.Provider<V, P> collectorProvider;
 
 	public LuceneObjectProjection(Builder builder, LuceneSearchProjection<?>[] inners,
-			ProjectionCompositor<E, V> compositor, ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
+			ProjectionCompositor<E, V> compositor, ProjectionCollector.Provider<V, P> collectorProvider) {
 		super( builder.scope );
 		this.absoluteFieldPath = builder.objectField.absolutePath();
 		this.nested = builder.objectField.type().nested();
 		this.filter = builder.filter;
 		this.nestedDocumentPath = builder.objectField.nestedDocumentPath();
-		this.requiredContextAbsoluteFieldPath = accumulatorProvider.isSingleValued()
+		this.requiredContextAbsoluteFieldPath = collectorProvider.isSingleValued()
 				? builder.objectField.closestMultiValuedParentAbsolutePath()
 				: null;
 		this.inners = inners;
 		this.compositor = compositor;
-		this.accumulatorProvider = accumulatorProvider;
+		this.collectorProvider = collectorProvider;
 	}
 
 	@Override
@@ -69,7 +69,7 @@ public String toString() {
 		return getClass().getSimpleName() + "["
 				+ "inners=" + Arrays.toString( inners )
 				+ ", compositor=" + compositor
-				+ ", accumulatorProvider=" + accumulatorProvider
+				+ ", collectorProvider=" + collectorProvider
 				+ "]";
 	}
 
@@ -86,7 +86,7 @@ public Extractor<?, P> request(ProjectionRequestContext context) {
 			innerExtractors[i] = inners[i].request( innerContext );
 		}
 		return new ObjectFieldExtractor<>( context.absoluteCurrentNestedFieldPath(), innerExtractors,
-				accumulatorProvider.get() );
+				collectorProvider.get() );
 	}
 
 	/**
@@ -95,13 +95,13 @@ public Extractor<?, P> request(ProjectionRequestContext context) {
 	private class ObjectFieldExtractor<A> implements Extractor<A, P> {
 		private final String contextAbsoluteFieldPath;
 		private final Extractor<?, ?>[] inners;
-		private final ProjectionAccumulator<E, V, A, P> accumulator;
+		private final ProjectionCollector<E, V, A, P> collector;
 
 		private ObjectFieldExtractor(String contextAbsoluteFieldPath,
-				Extractor<?, ?>[] inners, ProjectionAccumulator<E, V, A, P> accumulator) {
+				Extractor<?, ?>[] inners, ProjectionCollector<E, V, A, P> collector) {
 			this.contextAbsoluteFieldPath = contextAbsoluteFieldPath;
 			this.inners = inners;
-			this.accumulator = accumulator;
+			this.collector = collector;
 		}
 
 		@Override
@@ -109,7 +109,7 @@ public String toString() {
 			return getClass().getSimpleName() + "["
 					+ "inners=" + Arrays.toString( inners )
 					+ ", compositor=" + compositor
-					+ ", accumulator=" + accumulator
+					+ ", collector=" + collector
 					+ "]";
 		}
 
@@ -129,7 +129,7 @@ private class ObjectFieldValues extends AbstractNestingAwareAccumulatingValues<E
 			private BitSet filterMatchedBitSet;
 
 			private ObjectFieldValues(TopDocsDataCollectorExecutionContext context, Values<?>[] inners) {
-				super( contextAbsoluteFieldPath, nestedDocumentPath, ObjectFieldExtractor.this.accumulator, context );
+				super( contextAbsoluteFieldPath, nestedDocumentPath, ObjectFieldExtractor.this.collector, context );
 				this.inners = inners;
 				this.filterBitSetProducer = filter == null ? null : new QueryBitSetProducer( filter );
 
@@ -158,15 +158,15 @@ protected A accumulate(A accumulated, int docId) throws IOException {
 					Object extractedDataForInner = inners[i].get( docId );
 					components = compositor.set( components, i, extractedDataForInner );
 				}
-				return accumulator.accumulate( accumulated, components );
+				return collector.accumulate( accumulated, components );
 			}
 		}
 
 		@Override
 		public final P transform(LoadingResult<?> loadingResult, A accumulated,
 				ProjectionTransformContext context) {
-			for ( int i = 0; i < accumulator.size( accumulated ); i++ ) {
-				E transformedData = accumulator.get( accumulated, i );
+			for ( int i = 0; i < collector.size( accumulated ); i++ ) {
+				E transformedData = collector.get( accumulated, i );
 				// Transform in-place
 				for ( int j = 0; j < inners.length; j++ ) {
 					Object extractedDataForInner = compositor.get( transformedData, j );
@@ -174,9 +174,9 @@ public final P transform(LoadingResult<?> loadingResult, A accumulated,
 							extractedDataForInner, context );
 					transformedData = compositor.set( transformedData, j, transformedDataForInner );
 				}
-				accumulated = accumulator.transform( accumulated, i, compositor.finish( transformedData ) );
+				accumulated = collector.transform( accumulated, i, compositor.finish( transformedData ) );
 			}
-			return accumulator.finish( accumulated );
+			return collector.finish( accumulated );
 		}
 	}
 
@@ -222,8 +222,8 @@ static class Builder implements CompositeProjectionBuilder {
 
 		@Override
 		public <E, V, P> SearchProjection<P> build(SearchProjection<?>[] inners, ProjectionCompositor<E, V> compositor,
-				ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
-			if ( accumulatorProvider.isSingleValued() && objectField.multiValued() ) {
+				ProjectionCollector.Provider<V, P> collectorProvider) {
+			if ( collectorProvider.isSingleValued() && objectField.multiValued() ) {
 				throw log.invalidSingleValuedProjectionOnMultiValuedField( objectField.absolutePath(),
 						objectField.eventContext() );
 			}
@@ -233,7 +233,7 @@ public <E, V, P> SearchProjection<P> build(SearchProjection<?>[] inners, Project
 				typedInners[i] = LuceneSearchProjection.from( scope, inners[i] );
 			}
 			return new LuceneObjectProjection<>( this, typedInners,
-					compositor, accumulatorProvider );
+					compositor, collectorProvider );
 		}
 	}
 }
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/query/dsl/impl/LuceneSearchQuerySelectStepImpl.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/query/dsl/impl/LuceneSearchQuerySelectStepImpl.java
index ec231ab5ee9..4ed9a537a84 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/query/dsl/impl/LuceneSearchQuerySelectStepImpl.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/search/query/dsl/impl/LuceneSearchQuerySelectStepImpl.java
@@ -20,9 +20,9 @@
 import org.hibernate.search.engine.search.predicate.SearchPredicate;
 import org.hibernate.search.engine.search.predicate.dsl.PredicateFinalStep;
 import org.hibernate.search.engine.search.predicate.dsl.SimpleBooleanPredicateClausesCollector;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.dsl.ProjectionFinalStep;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionCompositor;
 import org.hibernate.search.engine.search.query.dsl.spi.AbstractSearchQuerySelectStep;
 
@@ -81,7 +81,7 @@ public <P> LuceneSearchQueryWhereStep<P, LOS> select(SearchProjection<P> project
 	public LuceneSearchQueryWhereStep<List<?>, LOS> select(SearchProjection<?>... projections) {
 		return select( scope.projectionBuilders().composite()
 				.build( projections, ProjectionCompositor.fromList( projections.length ),
-						ProjectionAccumulator.single() ) );
+						ProjectionCollector.nullable() ) );
 	}
 
 	@Override
diff --git a/documentation/src/main/asciidoc/migration/index.adoc b/documentation/src/main/asciidoc/migration/index.adoc
index 3b0d2205cb9..a577f290d5c 100644
--- a/documentation/src/main/asciidoc/migration/index.adoc
+++ b/documentation/src/main/asciidoc/migration/index.adoc
@@ -103,6 +103,10 @@ interfaces are removed in this version. They have their alternatives in a `org.h
 Instead, we are introducing the `org.hibernate.search.mapper.pojo.massindexing.MassIndexingTypeGroupMonitor`
 that can be obtained through `org.hibernate.search.mapper.pojo.massindexing.MassIndexingMonitor#typeGroupMonitor(..)`.
 This new type group monitor has more flexibility and also allows implementors to skip total count computations if needed.
+- `multi()` methods exposed in various projection DSL steps are deprecated in favour of a `collector(ProjectionCollector.Provider)`,
+or one of the "shortcut-methods": `.list()`/`.set()`/`.sortedSet()`...
+Check the `ProjectionCollector` factory methods to see the list of built-in collectors that provide support for nullable/optional single-valued projections
+and for multivalued ones such as lists, sets arrays and more.
 
 [[spi]]
 == SPI
diff --git a/documentation/src/main/asciidoc/public/reference/_binding-projection.adoc b/documentation/src/main/asciidoc/public/reference/_binding-projection.adoc
index e22843a0f61..3d0b956163c 100644
--- a/documentation/src/main/asciidoc/public/reference/_binding-projection.adoc
+++ b/documentation/src/main/asciidoc/public/reference/_binding-projection.adoc
@@ -87,10 +87,13 @@ include::{sourcedir}/org/hibernate/search/documentation/mapper/orm/binding/proje
 
 include::../components/_incubating-warning.adoc[]
 
-You can call `.multi()` on the context passed to the projection binder
-in order to discover whether the constructor parameter being bound is multi-valued
-(according to the same rules as <<mapping-projection-inner-inference-type,implicit inner projection inference>>),
-and to bind a multi-valued projection.
+You can call `.containerElement()` on the context passed to the projection binder
+in order to discover whether the constructor parameter being bound is some sort of container wrapping the value/values
+(according to the same rules as <<mapping-projection-inner-inference-type,implicit inner projection inference>>).
+If the returned value is a non-empty optional, then the `.constructorParameter()` will provide access to the container type in use.
+Additionally, the same context has access to a factory (`.projectionCollectorProviderFactory()`)
+from which a projection collector can be obtained based on a container and element types
+(if the container type is `null` then the factory will return the `nullable()` single-valued collector).
 
 .Implementing and using a `ProjectionBinder` supporting multi-valued projections
 ====
@@ -98,15 +101,18 @@ and to bind a multi-valued projection.
 ----
 include::{sourcedir}/org/hibernate/search/documentation/mapper/orm/binding/projectionbinder/multi/MyFieldProjectionBinder.java[tags=include]
 ----
-<1> `multi()` returns an optional that contains a context
-if and only if the constructor parameter is considered multi-valued.
-<2> Call `multi.definition(...)` to define the projection to use.
-<3> Here we're failing for single-valued constructor parameters,
-but we could theoreticall fall back to a single-valued projection.
-<4> The projection definition, being multi-valued,
-must implement `ProjectionDefinition<List<T>>`,
-where `T` is the exepected type of projected values,
+<1> `containerElement()` returns an optional that contains a type of the container elements
+if and only if the constructor parameter is considered as such that is wrapped in a container, e.g. a multivalued collection.
+<2> Call `context.definition(...)` to define the projection to use.
+<3> Here we're failing for single-valued (nullable) constructor parameters,
+but we could theoretically fall back to a single-valued projection using the `ProjectionCollector.nullable()`.
+<4> The projection definition, being multivalued,
+must implement `ProjectionDefinition<SomeCollection<T>>`,
+where `T` is the expected type of projected values,
+`SomeCollection` is one of the supported collection types available in `ProjectionCollector`,
 and must configure returned projections accordingly.
+If the required collection type is not present in the `ProjectionCollector`,
+then a custom projection collector provider can be supplied.
 
 [source, JAVA, indent=0, subs="+callouts"]
 ----
@@ -138,7 +144,8 @@ or by delegating to it in a custom projection definition.
 
 Other methods exposed on the binding context work similarly:
 
-* `.createObjectDefinitionMulti(...)` returns a <<binding-projection-multi,multi-valued>> object projection definition.
+* `.createObjectDefinition(..., ProjectionCollector.Provider)` returns an object projection definition with the provided collector applied
+and can be used for <<binding-projection-multi,multivalued>> object projections or object projections wrapped in some other containers.
 * `.createCompositeDefinition(...)` returns a (single-valued)
 <<search-dsl-projection-composite,composite projection>> definition
 (which, on contrary to an <<search-dsl-projection-object,object projection>>, is not bound to an object field in the index).
diff --git a/documentation/src/main/asciidoc/public/reference/_mapping-projection.adoc b/documentation/src/main/asciidoc/public/reference/_mapping-projection.adoc
index c246f389711..9eb26dfd6a1 100644
--- a/documentation/src/main/asciidoc/public/reference/_mapping-projection.adoc
+++ b/documentation/src/main/asciidoc/public/reference/_mapping-projection.adoc
@@ -39,7 +39,7 @@ See <<mapping-projection-inner-inference>> for more information on how construct
 +
 Alternatively, the field projection can be configured explicitly with <<search-dsl-projection-field-mapping,`@FieldProjection`>>.
 <4> To project on an object field, add a constructor parameter named after that field and with its own custom projection type.
-Multivalued projections <<mapping-projection-inner-inference-type,must be modeled as a `List<...>`>> or supertype.
+Multivalued projections <<mapping-projection-inner-inference-type,must be modeled as one of the multivalued containers for which a collector is available in `ProjectionCollector`>> or their supertype.
 +
 Alternatively, the object projection can be configured explicitly with <<search-dsl-projection-object-mapping,`@ObjectProjection`>>.
 <5> Annotate any custom projection type used for object fields with `@ProjectionConstructor` as well.
@@ -106,16 +106,23 @@ for the target field, which in general is the type of the property annotated wit
 (generally mapped using <<mapping-indexedembedded,`@IndexedEmbedded`>>),
 set the parameter type to another custom type annotated with `@ProjectionConstructor`,
 whose constructor will define which fields to extract from that object field.
-* For a multivalued projection, follow the rules above then wrap the type with `Iterable`, `Collection` or `List`,
-e.g. `Iterable<SomeType>`, `Collection<SomeType>` or `List<SomeType>`.
+* For projections where values are wrapped in a container, be it a multivalued projection represented by some collection or array,
+or a single-valued projection wrapped in an optional,
+follow the rules above for the elements inside the container and then wrap the type with one of the containers
+available in `ProjectionCollector` (`Iterable`, `Collection`, `List`, etc.),
+e.g. `Iterable<SomeType>`, `Collection<SomeType>`, `List<SomeType>`, etc.
 
 [IMPORTANT]
 ====
 Constructor parameters meant to represent a multivalued projection
-can **only** have the type `Iterable<...>`, `Collection<...>` or `List<...>`.
+**must** have the type of one of the supported multivalued containers.
+====
 
-Other container types such as `Map` or `Optional` are not supported
-https://hibernate.atlassian.net/browse/HSEARCH-4577[at the moment].
+[NOTE]
+====
+In case the `ProjectionCollector` does not provide a suitable collector for a container/collection
+needed for a constructor parameter mapping, <<binding-projection-multi,a custom projection binding>> can be implemented
+and a user-implemented projection collector applied.
 ====
 
 [[mapping-projection-inner-inference-fieldpath]]
diff --git a/documentation/src/main/asciidoc/public/reference/_search-dsl-projection.adoc b/documentation/src/main/asciidoc/public/reference/_search-dsl-projection.adoc
index a0a0c2a808e..af45e8c5870 100644
--- a/documentation/src/main/asciidoc/public/reference/_search-dsl-projection.adoc
+++ b/documentation/src/main/asciidoc/public/reference/_search-dsl-projection.adoc
@@ -72,7 +72,7 @@ See <<mapping-projection-inner-inference>> for more information on how construct
 +
 Alternatively, the field projection can be configured explicitly with <<search-dsl-projection-field-mapping,`@FieldProjection`>>.
 <4> To project on an object field, add a constructor parameter named after that field and with its own custom projection type.
-Multivalued projections <<mapping-projection-inner-inference-type,must be modeled as a `List<...>`>> or supertype.
+Multivalued projections <<mapping-projection-inner-inference-type,must be modeled as one of the multivalued containers available in `ProjectionCollector`>> or their supertype.
 +
 Alternatively, the object projection can be configured explicitly with <<search-dsl-projection-object-mapping,`@ObjectProjection`>>.
 <5> Annotate any custom projection type used for object fields with `@ProjectionConstructor` as well.
@@ -403,8 +403,8 @@ include::{sourcedir}/org/hibernate/search/documentation/search/projection/Projec
 [[search-dsl-projection-field-multivalued]]
 === Multivalued fields
 
-To return multiple values, and thus allow projection on multivalued fields, use `.multi()`.
-This will change the return type of the projection to `List<T>` where `T` is what the single-valued projection
+To return multiple values, and thus allow projection on multivalued fields, use `.collector(..)`.
+This will change the return type of the projection to `SomeContainer<T>` where `T` is what the single-valued projection
 would have returned.
 
 .Returning field values from matched documents, for multivalued fields
@@ -610,8 +610,8 @@ include::{sourcedir}/org/hibernate/search/documentation/search/projection/Projec
 [[search-dsl-projection-distance-multivalued]]
 === Multivalued fields
 
-To return multiple values, and thus allow projection on multivalued fields, use `.multi()`.
-This will change the return type of the projection to `List<Double>`.
+To return multiple values, and thus allow projection on multivalued fields, use `.collector(..)`.
+This will change the return type of the projection to `SomeContainer<Double>`.
 
 .Returning the distance to a point, for multivalued fields
 ====
@@ -834,7 +834,7 @@ See <<mapping-projection-inner-inference>> for more information on how construct
 +
 Alternatively, the field projection can be configured explicitly with <<search-dsl-projection-field-mapping,`@FieldProjection`>>.
 <4> To project on an object field, add a constructor parameter named after that field and with its own custom projection type.
-Multivalued projections <<mapping-projection-inner-inference-type,must be modeled as a `List<...>`>> or supertype.
+Multivalued projections <<mapping-projection-inner-inference-type,must be modeled as one of the multivalued containers for which a collector is available in `ProjectionCollector`>> or their supertype.
 +
 Alternatively, the object projection can be configured explicitly with <<search-dsl-projection-object-mapping,`@ObjectProjection`>>.
 <5> Annotate any custom projection type used for object fields with `@ProjectionConstructor` as well.
diff --git a/documentation/src/test/java/org/hibernate/search/documentation/mapper/orm/binding/projectionbinder/multi/MyFieldProjectionBinder.java b/documentation/src/test/java/org/hibernate/search/documentation/mapper/orm/binding/projectionbinder/multi/MyFieldProjectionBinder.java
index be6328e06e1..c11f9ebfe24 100644
--- a/documentation/src/test/java/org/hibernate/search/documentation/mapper/orm/binding/projectionbinder/multi/MyFieldProjectionBinder.java
+++ b/documentation/src/test/java/org/hibernate/search/documentation/mapper/orm/binding/projectionbinder/multi/MyFieldProjectionBinder.java
@@ -7,24 +7,25 @@
 import java.util.List;
 import java.util.Optional;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.definition.ProjectionDefinition;
 import org.hibernate.search.engine.search.projection.definition.ProjectionDefinitionContext;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
+import org.hibernate.search.mapper.pojo.model.PojoModelValue;
 import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBinder;
 import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBindingContext;
-import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBindingMultiContext;
 
 //tag::include[]
 public class MyFieldProjectionBinder implements ProjectionBinder {
 	@Override
 	public void bind(ProjectionBindingContext context) {
-		Optional<? extends ProjectionBindingMultiContext> multi = context.multi(); // <1>
-		if ( multi.isPresent() ) {
-			multi.get().definition( String.class, new MyProjectionDefinition() ); // <2>
+		Optional<PojoModelValue<?>> containerElement = context.containerElement(); // <1>
+		if ( containerElement.isPresent() ) {
+			context.definition( String.class, new MyProjectionDefinition() ); // <2>
 		}
 		else {
-			throw new RuntimeException( "This binder only supports multi-valued constructor parameters" ); // <3>
+			throw new RuntimeException( "This binder only supports container-wrapped constructor parameters" ); // <3>
 		}
 	}
 
@@ -34,7 +35,7 @@ private static class MyProjectionDefinition
 		public SearchProjection<List<String>> create(SearchProjectionFactory<?, ?> factory,
 				ProjectionDefinitionContext context) {
 			return factory.field( "tags", String.class )
-					.multi() // <4>
+					.collector( ProjectionCollector.list() ) // <4>
 					.toProjection();
 		}
 	}
diff --git a/documentation/src/test/java/org/hibernate/search/documentation/mapper/orm/projection/ProjectionConstructorMappingJava17IT.java b/documentation/src/test/java/org/hibernate/search/documentation/mapper/orm/projection/ProjectionConstructorMappingJava17IT.java
index 0bbc40364c3..5488dc5a9cd 100644
--- a/documentation/src/test/java/org/hibernate/search/documentation/mapper/orm/projection/ProjectionConstructorMappingJava17IT.java
+++ b/documentation/src/test/java/org/hibernate/search/documentation/mapper/orm/projection/ProjectionConstructorMappingJava17IT.java
@@ -16,6 +16,7 @@
 import org.hibernate.search.documentation.testsupport.DocumentationSetupHelper;
 import org.hibernate.search.engine.backend.types.ObjectStructure;
 import org.hibernate.search.engine.backend.types.Projectable;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.mapper.orm.Search;
 import org.hibernate.search.mapper.orm.session.SearchSession;
 import org.hibernate.search.mapper.pojo.mapping.definition.programmatic.TypeMappingStep;
@@ -144,7 +145,7 @@ void simple(DocumentationSetupHelper.SetupVariant variant) {
 													f.field( "authors.lastName", String.class )
 											)
 											.as( MyBookProjection.Author::new )
-											.multi()
+											.collector( ProjectionCollector.list() )
 							)
 							.as( MyBookProjection::new ) )
 					.where( f -> f.matchAll() )
diff --git a/documentation/src/test/java/org/hibernate/search/documentation/search/projection/MyBookTitleAndAuthorNamesInSetProjection.java b/documentation/src/test/java/org/hibernate/search/documentation/search/projection/MyBookTitleAndAuthorNamesInSetProjection.java
new file mode 100644
index 00000000000..9b5d802d820
--- /dev/null
+++ b/documentation/src/test/java/org/hibernate/search/documentation/search/projection/MyBookTitleAndAuthorNamesInSetProjection.java
@@ -0,0 +1,23 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.documentation.search.projection;
+
+import java.util.Set;
+
+import org.hibernate.search.mapper.pojo.mapping.definition.annotation.FieldProjection;
+import org.hibernate.search.mapper.pojo.mapping.definition.annotation.ProjectionConstructor;
+
+// @formatter:off
+//tag::include[]
+@ProjectionConstructor // <1>
+public record MyBookTitleAndAuthorNamesInSetProjection(
+		@FieldProjection // <2>
+		String title, // <3>
+		@FieldProjection(path = "authors.lastName") // <4>
+		Set<String> authorLastNames // <5>
+) {
+}
+//end::include[]
+// @formatter:on
diff --git a/documentation/src/test/java/org/hibernate/search/documentation/search/projection/ProjectionDslIT.java b/documentation/src/test/java/org/hibernate/search/documentation/search/projection/ProjectionDslIT.java
index 51f29d3c9df..2801f65fc0f 100644
--- a/documentation/src/test/java/org/hibernate/search/documentation/search/projection/ProjectionDslIT.java
+++ b/documentation/src/test/java/org/hibernate/search/documentation/search/projection/ProjectionDslIT.java
@@ -27,6 +27,7 @@
 import org.hibernate.search.engine.backend.common.DocumentReference;
 import org.hibernate.search.engine.common.EntityReference;
 import org.hibernate.search.engine.search.common.ValueModel;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.query.SearchResult;
 import org.hibernate.search.engine.spatial.DistanceUnit;
 import org.hibernate.search.engine.spatial.GeoPoint;
@@ -240,7 +241,7 @@ void field() {
 		withinSearchSession( searchSession -> {
 			// tag::field-multiValued[]
 			List<List<String>> hits = searchSession.search( Book.class )
-					.select( f -> f.field( "authors.lastName", String.class ).multi() )
+					.select( f -> f.field( "authors.lastName", String.class ).collector( ProjectionCollector.list() ) )
 					.where( f -> f.matchAll() )
 					.fetchHits( 20 );
 			// end::field-multiValued[]
@@ -333,7 +334,7 @@ void distance() {
 			// tag::distance-multiValued[]
 			GeoPoint center = GeoPoint.of( 47.506060, 2.473916 );
 			SearchResult<List<Double>> result = searchSession.search( Book.class )
-					.select( f -> f.distance( "authors.placeOfBirth", center ).multi() )
+					.select( f -> f.distance( "authors.placeOfBirth", center ).collector( ProjectionCollector.list() ) )
 					.where( f -> f.matchAll() )
 					.fetch( 20 );
 			// end::distance-multiValued[]
@@ -580,7 +581,7 @@ void object() {
 							.from( f.field( "authors.firstName", String.class ), // <2>
 									f.field( "authors.lastName", String.class ) ) // <3>
 							.as( MyAuthorName::new ) // <4>
-							.multi() ) // <5>
+							.collector( ProjectionCollector.list() ) ) // <5>
 					.where( f -> f.matchAll() )
 					.fetchHits( 20 ); // <6>
 			// end::object-customObject[]
@@ -630,7 +631,7 @@ void object() {
 									new MyAuthorNameAndBirthDateAndPlaceOfBirthDistance(
 											(String) list.get( 0 ), (String) list.get( 1 ),
 											(LocalDate) list.get( 2 ), (Double) list.get( 3 ) ) )
-							.multi() ) // <7>
+							.collector( ProjectionCollector.list() ) ) // <7>
 					.where( f -> f.matchAll() )
 					.fetchHits( 20 ); // <8>
 			// end::object-customObject-asList[]
@@ -692,7 +693,7 @@ void object() {
 									new MyAuthorNameAndBirthDateAndPlaceOfBirthDistance(
 											(String) array[0], (String) array[1],
 											(LocalDate) array[2], (Double) array[3] ) )
-							.multi() ) // <7>
+							.collector( ProjectionCollector.list() ) ) // <7>
 					.where( f -> f.matchAll() )
 					.fetchHits( 20 ); // <8>
 			// end::object-customObject-asArray[]
@@ -745,7 +746,7 @@ void object() {
 							.from( f.field( "authors.firstName", String.class ), // <2>
 									f.field( "authors.lastName", String.class ) ) // <3>
 							.asList() // <4>
-							.multi() ) // <5>
+							.collector( ProjectionCollector.list() ) ) // <5>
 					.where( f -> f.matchAll() )
 					.fetchHits( 20 ); // <6>
 			// end::object-list[]
@@ -785,7 +786,7 @@ void object() {
 							.from( f.field( "authors.firstName", String.class ), // <2>
 									f.field( "authors.lastName", String.class ) ) // <3>
 							.asArray() // <4>
-							.multi() ) // <5>
+							.collector( ProjectionCollector.list() ) ) // <5>
 					.where( f -> f.matchAll() )
 					.fetchHits( 20 ); // <6>
 			// end::object-array[]
diff --git a/documentation/src/test/java/org/hibernate/search/documentation/search/projection/ProjectionDslJava17IT.java b/documentation/src/test/java/org/hibernate/search/documentation/search/projection/ProjectionDslJava17IT.java
index 150e41ff981..634b18115b5 100644
--- a/documentation/src/test/java/org/hibernate/search/documentation/search/projection/ProjectionDslJava17IT.java
+++ b/documentation/src/test/java/org/hibernate/search/documentation/search/projection/ProjectionDslJava17IT.java
@@ -20,6 +20,7 @@
 import org.hibernate.search.documentation.testsupport.DocumentationSetupHelper;
 import org.hibernate.search.engine.backend.types.ObjectStructure;
 import org.hibernate.search.engine.backend.types.Projectable;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.spatial.GeoPoint;
 import org.hibernate.search.mapper.orm.Search;
 import org.hibernate.search.mapper.orm.session.SearchSession;
@@ -62,8 +63,7 @@ public static List<? extends Arguments> params() {
 				// This wouldn't be needed in a typical application.
 				CollectionHelper.asSet( MyBookProjection.class, MyBookProjection.Author.class, MyAuthorProjection.class,
 						MyBookIdAndTitleProjection.class, MyBookTitleAndAuthorNamesProjection.class,
-						MyBookTitleAndAuthorsProjection.class,
-						MyBookIdAndTitleProjection.class, MyBookTitleAndAuthorNamesProjection.class,
+						MyBookTitleAndAuthorsProjection.class, MyBookTitleAndAuthorNamesInSetProjection.class,
 						MyBookScoreAndTitleProjection.class,
 						MyBookDocRefAndTitleProjection.class,
 						MyBookEntityAndTitleProjection.class,
@@ -136,6 +136,15 @@ public static List<? extends Arguments> params() {
 							.projection( FieldProjectionBinder.create( "authors.lastName" ) );
 					//end::programmatic-field-projection[]
 
+					TypeMappingStep myBookTitleAndAuthorNamesInSetProjectionMapping =
+							mapping.type( MyBookTitleAndAuthorNamesInSetProjection.class );
+					myBookTitleAndAuthorNamesInSetProjectionMapping.mainConstructor()
+							.projectionConstructor();
+					myBookTitleAndAuthorNamesInSetProjectionMapping.mainConstructor().parameter( 0 )
+							.projection( FieldProjectionBinder.create() );
+					myBookTitleAndAuthorNamesInSetProjectionMapping.mainConstructor().parameter( 1 )
+							.projection( FieldProjectionBinder.create( "authors.lastName" ) );
+
 					//tag::programmatic-score-projection[]
 					TypeMappingStep myBookScoreAndTitleProjection =
 							mapping.type( MyBookScoreAndTitleProjection.class );
@@ -299,7 +308,7 @@ void object_mapped_record(DocumentationSetupHelper.SetupVariant variant) {
 			List<List<MyAuthorProjection>> hits = searchSession.search( Book.class )
 					.select( f -> f.object( "authors" ) // <1>
 							.as( MyAuthorProjection.class ) // <2>
-							.multi() ) // <3>
+							.collector( ProjectionCollector.list() ) ) // <3>
 					.where( f -> f.matchAll() )
 					.fetchHits( 20 ); // <4>
 			// end::object-mapped-record[]
@@ -364,6 +373,32 @@ void projectionConstructor_field(DocumentationSetupHelper.SetupVariant variant)
 		} );
 	}
 
+	@ParameterizedTest(name = "{0}")
+	@MethodSource("params")
+	void projectionConstructor_field_set(DocumentationSetupHelper.SetupVariant variant) {
+		init( variant );
+		with( entityManagerFactory ).runInTransaction( entityManager -> {
+			SearchSession searchSession = Search.session( entityManager );
+
+			// tag::projection-constructor-field-set[]
+			List<MyBookTitleAndAuthorNamesInSetProjection> hits = searchSession.search( Book.class )
+					.select( MyBookTitleAndAuthorNamesInSetProjection.class )// <1>
+					.where( f -> f.matchAll() )
+					.fetchHits( 20 ); // <2>
+			// end::projection-constructor-field-set[]
+			assertThat( hits ).containsExactlyInAnyOrderElementsOf(
+					entityManager.createQuery( "select b from Book b", Book.class ).getResultList().stream()
+							.map( book -> new MyBookTitleAndAuthorNamesInSetProjection(
+									book.getTitle(),
+									book.getAuthors().stream()
+											.map( Author::getLastName )
+											.collect( Collectors.toSet() )
+							) )
+							.collect( Collectors.toList() )
+			);
+		} );
+	}
+
 	@ParameterizedTest(name = "{0}")
 	@MethodSource("params")
 	void projectionConstructor_score(DocumentationSetupHelper.SetupVariant variant) {
diff --git a/engine/src/main/java/org/hibernate/search/engine/backend/types/converter/spi/ProjectionConverter.java b/engine/src/main/java/org/hibernate/search/engine/backend/types/converter/spi/ProjectionConverter.java
index 6952c3ecec2..6d251f84014 100644
--- a/engine/src/main/java/org/hibernate/search/engine/backend/types/converter/spi/ProjectionConverter.java
+++ b/engine/src/main/java/org/hibernate/search/engine/backend/types/converter/spi/ProjectionConverter.java
@@ -88,4 +88,11 @@ public boolean isCompatibleWith(ProjectionConverter<?, ?> other) {
 		return delegate.isCompatibleWith( other.delegate );
 	}
 
+
+	/**
+	 * @return The document value converter that is backing up this converter.
+	 */
+	public FromDocumentValueConverter<? super F, V> delegate() {
+		return delegate;
+	}
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/ProjectionCollector.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/ProjectionCollector.java
new file mode 100644
index 00000000000..60b091cf715
--- /dev/null
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/ProjectionCollector.java
@@ -0,0 +1,253 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.engine.search.projection;
+
+import java.util.Collection;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import java.util.SortedSet;
+import java.util.function.Function;
+
+import org.hibernate.search.engine.backend.types.converter.FromDocumentValueConverter;
+import org.hibernate.search.engine.backend.types.converter.runtime.FromDocumentValueConvertContext;
+import org.hibernate.search.engine.search.projection.spi.BuiltInProjectionCollectors;
+import org.hibernate.search.util.common.annotation.Incubating;
+
+/**
+ * A variation on {@link java.util.stream.Collector} suitable for projections on field values.
+ * <p>
+ * Compared to {@link java.util.stream.Collector}:
+ * <ul>
+ *     <li>There is no concept of parallel execution.</li>
+ *     <li>All operations are expected to be non-blocking,
+ *     except for {@link #transformAll(Object, FromDocumentValueConverter, FromDocumentValueConvertContext)}
+ *     and {@link #finish(Object)}.</li>
+ *     <li>Values to accumulate are expected to be {@link #transform(Object, int, Object) transformed} exactly once
+ *     after accumulation, changing their type from {@link E} to {@link V}.
+ *     Clients are responsible for ensuring values to accumulate have been transformed
+ *     upon calling {@link #finish(Object)}.
+ * </ul>
+ *
+ * @param <E> The type of extracted values to accumulate before being transformed.
+ * @param <V> The type of values to accumulate obtained by transforming extracted values ({@code E}).
+ * @param <A> The type of the temporary storage for accumulated values,
+ * before and after being transformed.
+ * @param <R> The type of the final result containing values of type {@code V}.
+ */
+@Incubating
+public interface ProjectionCollector<E, V, A, R> {
+
+	/**
+	 * @return The projection collector capable of accumulating single-valued projections in an as-is form,
+	 * i.e. the value is returned without any extra transformations.
+	 * @param <V> The type of values to accumulate.
+	 */
+	static <V> ProjectionCollector.Provider<V, V> nullable() {
+		return BuiltInProjectionCollectors.nullable();
+	}
+
+	/**
+	 * @return The projection collector capable of accumulating single-valued projections and wrapping the values in an {@link Optional}.
+	 * @param <V> The type of values to accumulate.
+	 */
+	static <V> Provider<V, Optional<V>> optional() {
+		return BuiltInProjectionCollectors.optional();
+	}
+
+	/**
+	 * @param converter The function that defines how to convert a list of collected values to the final collection.
+	 * @return An collector based on a list as a temporary storage.
+	 * @param <V> The type of values to accumulate.
+	 * @param <C> The type of the resulting collection.
+	 */
+	static <V, C> Provider<V, C> simple(Function<List<V>, C> converter) {
+		return BuiltInProjectionCollectors.simple( converter );
+	}
+
+	/**
+	 * @return The projection collector capable of accumulating multivalued projections as a {@link List}.
+	 * @param <V> The type of values to accumulate.
+	 */
+	static <V> Provider<V, List<V>> list() {
+		return BuiltInProjectionCollectors.list();
+	}
+
+	/**
+	 * @return The projection collector capable of accumulating multivalued projections as a {@link Set}.
+	 * @param <V> The type of values to accumulate.
+	 */
+	static <V> Provider<V, Set<V>> set() {
+		return BuiltInProjectionCollectors.set();
+	}
+
+	/**
+	 * @return The projection collector capable of accumulating multivalued projections as a {@link SortedSet}.
+	 * @param <V> The type of values to accumulate.
+	 */
+	static <V> Provider<V, SortedSet<V>> sortedSet() {
+		return BuiltInProjectionCollectors.sortedSet();
+	}
+
+	/**
+	 * @return The projection collector capable of accumulating multivalued projections as a {@link SortedSet}
+	 * using a custom comparator.
+	 * @param comparator The comparator which should be used by the sorted set.
+	 * @param <V> The type of values to accumulate.
+	 */
+	static <V> Provider<V, SortedSet<V>> sortedSet(Comparator<? super V> comparator) {
+		return BuiltInProjectionCollectors.sortedSet( comparator );
+	}
+
+	/**
+	 * @return The projection collector capable of accumulating multivalued projections as an array.
+	 * @param componentType The type of the array elements.
+	 * @param <V> The type of values to accumulate.
+	 */
+	static <V> Provider<V, V[]> array(Class<? super V> componentType) {
+		return BuiltInProjectionCollectors.array( componentType );
+	}
+
+	/**
+	 * Creates the initial accumulated container.
+	 * <p>
+	 * This operation should be non-blocking.
+	 *
+	 * @return The initial accumulated container,
+	 * to pass to the first call to {@link #accumulate(Object, Object)}.
+	 */
+	A createInitial();
+
+	/**
+	 * Folds a new value in the given accumulated container.
+	 * <p>
+	 * This operation should be non-blocking.
+	 *
+	 * @param accumulated The accumulated value so far.
+	 * For the first call, this is a value returned by {@link #createInitial()}.
+	 * For the next calls, this is the value returned by the previous call to {@link #accumulate(Object, Object)}.
+	 * @param value The value to accumulate.
+	 * @return The new accumulated value.
+	 */
+	A accumulate(A accumulated, E value);
+
+	/**
+	 * Folds a collection of new values in the given accumulated container.
+	 * <p>
+	 * This operation should be non-blocking.
+	 *
+	 * @param accumulated The accumulated value so far.
+	 * For the first call, this is a value returned by {@link #createInitial()}.
+	 * For the next calls, this is the value returned by the previous call to {@link #accumulate(Object, Object)}.
+	 * @param values The values to accumulate.
+	 * @return The new accumulated value.
+	 */
+	default A accumulateAll(A accumulated, Collection<E> values) {
+		for ( E value : values ) {
+			accumulated = accumulate( accumulated, value );
+		}
+		return accumulated;
+	}
+
+	/**
+	 * @param accumulated The accumulated value so far,
+	 * returned by the last call to {@link #accumulate(Object, Object)}.
+	 * @return The number of elements in the accumulated value.
+	 */
+	int size(A accumulated);
+
+	/**
+	 * Retrieves the value at the given index.
+	 * <p>
+	 * This operation should be non-blocking.
+	 *
+	 * @param accumulated The accumulated value so far,
+	 * returned by the last call to {@link #accumulate(Object, Object)}.
+	 * @param index The index of the value to retrieve.
+	 * @return The value at the given index.
+	 */
+	E get(A accumulated, int index);
+
+	/**
+	 * Transforms the value at the given index,
+	 * replacing it with the given transformed value.
+	 * <p>
+	 * This operation should be non-blocking.
+	 *
+	 * @param accumulated The accumulated value so far,
+	 * returned by the last call to {@link #accumulate(Object, Object)}.
+	 * @param index The index of the value being transformed.
+	 * @param transformed The transformed value.
+	 * @return The new accumulated value.
+	 */
+	A transform(A accumulated, int index, V transformed);
+
+	/**
+	 * Transforms all values with the given converter and the given context.
+	 * <p>
+	 * This operation may be blocking.
+	 *
+	 * @param accumulated The accumulated value so far,
+	 * returned by the last call to {@link #accumulate(Object, Object)}.
+	 * @param converter The projection converter (from {@code F} to {@code V}).
+	 * @param context The context to be passed to the projection converter.
+	 * @return The new accumulated value.
+	 */
+	default A transformAll(A accumulated, FromDocumentValueConverter<? super E, ? extends V> converter,
+			FromDocumentValueConvertContext context) {
+		for ( int i = 0; i < size( accumulated ); i++ ) {
+			E initial = get( accumulated, i );
+			V transformed = converter.fromDocumentValue( initial, context );
+			accumulated = transform( accumulated, i, transformed );
+		}
+		return accumulated;
+	}
+
+	/**
+	 * Finishes the accumulation, converting the accumulated container into the final result.
+	 * <p>
+	 * This operation may be blocking.
+	 *
+	 * @param accumulated The temporary storage created by {@link #createInitial()},
+	 * then populated by successive calls to {@link #accumulate(Object, Object)},
+	 * then transformed by a single call to {@link #transformAll(Object, FromDocumentValueConverter, FromDocumentValueConvertContext)}
+	 * or by successive calls to {@link #transform(Object, int, Object)}.
+	 * @return The final result of the accumulation.
+	 */
+	R finish(A accumulated);
+
+	/**
+	 * @return An "empty" final value, i.e. when a {@link #finish(Object) final transformation}
+	 * is applied to {@link #createInitial() the initial value}.
+	 */
+	default R empty() {
+		return finish( createInitial() );
+	}
+
+	/**
+	 * Provides a collector for a given type of values to accumulate ({@code T}).
+	 * <p>
+	 * The provider may always return the same collector,
+	 * if generics are irrelevant and it's safe to do so.
+	 *
+	 * @param <U> The type of values to accumulate after being transformed.
+	 * @param <R> The type of the final result containing values of type {@code V}.
+	 */
+	interface Provider<U, R> {
+		/**
+		 * @param <T> The type of values to accumulate before being transformed.
+		 * @return A collector for the given type.
+		 */
+		<T> ProjectionCollector<T, U, ?, R> get();
+
+		/**
+		 * @return {@code true} if collectors returned by {@link #get()} can only accept a single value,
+		 * and will fail beyond that.
+		 */
+		boolean isSingleValued();
+	}
+
+}
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/ProjectionCollectorProviderFactory.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/ProjectionCollectorProviderFactory.java
new file mode 100644
index 00000000000..821d8021342
--- /dev/null
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/ProjectionCollectorProviderFactory.java
@@ -0,0 +1,27 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.engine.search.projection;
+
+import org.hibernate.search.util.common.annotation.Incubating;
+
+/**
+ * Defines the factory that can create {@link ProjectionCollector.Provider projection collector providers} based
+ * on a container type {@code R} and container element type {@code U}.
+ */
+@Incubating
+public interface ProjectionCollectorProviderFactory {
+	/**
+	 *
+	 * @param containerType The type of the expected container.
+	 * Passing a {@code null} value as a container type will result in {@link ProjectionCollector#nullable() a nullable collector}
+	 * being returned, i.e. a collector that does not wrap the value in any sort of container.
+	 * @param containerElementType The type of the container elements
+	 * @return The projection collector provider for a requested container/element types.
+	 * @param <U> The type of values to collector after being transformed.
+	 * @param <R> The type of the final result containing values of type {@code V}.
+	 */
+	<R, U> ProjectionCollector.Provider<U, R> projectionCollectorProvider(Class<R> containerType,
+			Class<U> containerElementType);
+}
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/ConstantProjectionDefinition.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/ConstantProjectionDefinition.java
index f03fc888486..a931329c1a4 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/ConstantProjectionDefinition.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/ConstantProjectionDefinition.java
@@ -6,8 +6,12 @@
 
 import java.util.Collections;
 import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import java.util.SortedSet;
 
 import org.hibernate.search.engine.environment.bean.BeanHolder;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.definition.ProjectionDefinitionContext;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
@@ -22,17 +26,53 @@ public final class ConstantProjectionDefinition<T> extends AbstractProjectionDef
 	@SuppressWarnings("rawtypes")
 	private static final BeanHolder<? extends ConstantProjectionDefinition> EMPTY_LIST_INSTANCE =
 			BeanHolder.of( new ConstantProjectionDefinition<List>( Collections.emptyList() ) );
+	@SuppressWarnings("rawtypes")
+	private static final BeanHolder<? extends ConstantProjectionDefinition> EMPTY_SET_INSTANCE =
+			BeanHolder.of( new ConstantProjectionDefinition<Set>( Collections.emptySet() ) );
+	@SuppressWarnings("rawtypes")
+	private static final BeanHolder<? extends ConstantProjectionDefinition> EMPTY_SORTED_SET_INSTANCE =
+			BeanHolder.of( new ConstantProjectionDefinition<SortedSet>( Collections.emptySortedSet() ) );
+	@SuppressWarnings("rawtypes")
+	private static final BeanHolder<? extends ConstantProjectionDefinition> OPTIONAL_EMPTY_INSTANCE =
+			BeanHolder.of( new ConstantProjectionDefinition<Optional>( Optional.empty() ) );
 
 	@SuppressWarnings("unchecked") // NULL_VALUE_INSTANCE works for any T
 	public static <T> BeanHolder<ConstantProjectionDefinition<T>> nullValue() {
 		return (BeanHolder<ConstantProjectionDefinition<T>>) NULL_VALUE_INSTANCE;
 	}
 
+	/**
+	 * @deprecated Use {@link #empty(ProjectionCollector.Provider)} instead.
+	 */
+	@Deprecated(since = "8.0")
 	@SuppressWarnings("unchecked") // EMPTY_LIST_INSTANCE works for any T
 	public static <T> BeanHolder<ConstantProjectionDefinition<List<T>>> emptyList() {
 		return (BeanHolder<ConstantProjectionDefinition<List<T>>>) EMPTY_LIST_INSTANCE;
 	}
 
+	@SuppressWarnings("unchecked") // empty collections works for any T
+	public static <T> BeanHolder<ConstantProjectionDefinition<T>> empty(ProjectionCollector.Provider<?, T> collector) {
+		T empty = collector.get().empty();
+
+		if ( ProjectionCollector.nullable().equals( collector ) ) {
+			return nullValue();
+		}
+		if ( ProjectionCollector.optional().equals( collector ) ) {
+			return (BeanHolder<ConstantProjectionDefinition<T>>) OPTIONAL_EMPTY_INSTANCE;
+		}
+		if ( ProjectionCollector.list().equals( collector ) ) {
+			return (BeanHolder<ConstantProjectionDefinition<T>>) EMPTY_LIST_INSTANCE;
+		}
+		if ( ProjectionCollector.set().equals( collector ) ) {
+			return (BeanHolder<ConstantProjectionDefinition<T>>) EMPTY_SET_INSTANCE;
+		}
+		if ( empty instanceof SortedSet ) {
+			return (BeanHolder<ConstantProjectionDefinition<T>>) EMPTY_SORTED_SET_INSTANCE;
+		}
+
+		return BeanHolder.of( new ConstantProjectionDefinition<>( empty ) );
+	}
+
 	private final T value;
 
 	private ConstantProjectionDefinition(T value) {
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/DistanceProjectionDefinition.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/DistanceProjectionDefinition.java
index 10438863b3e..e1d2b39442b 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/DistanceProjectionDefinition.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/DistanceProjectionDefinition.java
@@ -6,6 +6,7 @@
 
 import java.util.List;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.definition.ProjectionDefinitionContext;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
@@ -42,6 +43,7 @@ public void appendTo(ToStringTreeAppender appender) {
 
 	protected abstract boolean multi();
 
+	@Deprecated(since = "8.0")
 	@Incubating
 	public static final class SingleValued extends DistanceProjectionDefinition<Double> {
 		public SingleValued(String fieldPath, String parameterName, DistanceUnit unit) {
@@ -62,8 +64,10 @@ public SearchProjection<Double> create(SearchProjectionFactory<?, ?> factory, Pr
 		}
 	}
 
+	@Deprecated(since = "8.0")
 	@Incubating
 	public static final class MultiValued extends DistanceProjectionDefinition<List<Double>> {
+
 		public MultiValued(String fieldPath, String parameterName, DistanceUnit unit) {
 			super( fieldPath, parameterName, unit );
 		}
@@ -78,7 +82,33 @@ public SearchProjection<List<Double>> create(SearchProjectionFactory<?, ?> facto
 				ProjectionDefinitionContext context) {
 			return factory.withParameters( params -> factory
 					.distance( fieldPath, params.get( parameterName, GeoPoint.class ) )
-					.multi()
+					.collector( ProjectionCollector.list() )
+					.unit( unit )
+			).toProjection();
+		}
+	}
+
+	@Incubating
+	public static final class WrappedValued<C> extends DistanceProjectionDefinition<C> {
+		private final ProjectionCollector.Provider<Double, C> collector;
+
+		public WrappedValued(String fieldPath, String parameterName, DistanceUnit unit,
+				ProjectionCollector.Provider<Double, C> collector) {
+			super( fieldPath, parameterName, unit );
+			this.collector = collector;
+		}
+
+		@Override
+		protected boolean multi() {
+			return !collector.isSingleValued();
+		}
+
+		@Override
+		public SearchProjection<C> create(SearchProjectionFactory<?, ?> factory,
+				ProjectionDefinitionContext context) {
+			return factory.withParameters( params -> factory
+					.distance( fieldPath, params.get( parameterName, GeoPoint.class ) )
+					.collector( collector )
 					.unit( unit )
 			).toProjection();
 		}
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/FieldProjectionDefinition.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/FieldProjectionDefinition.java
index 1f704bbac5c..b19befe9fc6 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/FieldProjectionDefinition.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/FieldProjectionDefinition.java
@@ -7,6 +7,7 @@
 import java.util.List;
 
 import org.hibernate.search.engine.search.common.ValueModel;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.definition.ProjectionDefinitionContext;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
@@ -42,6 +43,7 @@ public void appendTo(ToStringTreeAppender appender) {
 
 	protected abstract boolean multi();
 
+	@Deprecated(since = "8.0")
 	@Incubating
 	public static final class SingleValued<F> extends FieldProjectionDefinition<F, F> {
 		public SingleValued(String fieldPath, Class<F> fieldType, ValueModel valueModel) {
@@ -60,8 +62,10 @@ public SearchProjection<F> create(SearchProjectionFactory<?, ?> factory,
 		}
 	}
 
+	@Deprecated(since = "8.0")
 	@Incubating
 	public static final class MultiValued<F> extends FieldProjectionDefinition<List<F>, F> {
+
 		public MultiValued(String fieldPath, Class<F> fieldType, ValueModel valueModel) {
 			super( fieldPath, fieldType, valueModel );
 		}
@@ -72,9 +76,32 @@ protected boolean multi() {
 		}
 
 		@Override
-		public SearchProjection<List<F>> create(SearchProjectionFactory<?, ?> factory,
+		public SearchProjection<List<F>> create(SearchProjectionFactory<?, ?> factory, ProjectionDefinitionContext context) {
+			return factory.field( fieldPath, fieldType, valueModel )
+					.collector( ProjectionCollector.list() ).toProjection();
+		}
+	}
+
+	@Incubating
+	public static final class AccumulatedValued<C, F> extends FieldProjectionDefinition<C, F> {
+		private final ProjectionCollector.Provider<F, C> collector;
+
+		public AccumulatedValued(String fieldPath, Class<F> fieldType, ProjectionCollector.Provider<F, C> collector,
+				ValueModel valueModel) {
+			super( fieldPath, fieldType, valueModel );
+			this.collector = collector;
+		}
+
+		@Override
+		protected boolean multi() {
+			return !collector.isSingleValued();
+		}
+
+		@Override
+		public SearchProjection<C> create(SearchProjectionFactory<?, ?> factory,
 				ProjectionDefinitionContext context) {
-			return factory.field( fieldPath, fieldType, valueModel ).multi().toProjection();
+			return factory.field( fieldPath, fieldType, valueModel )
+					.collector( collector ).toProjection();
 		}
 	}
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/ObjectProjectionDefinition.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/ObjectProjectionDefinition.java
index c98e858a37f..05c57bf3de4 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/ObjectProjectionDefinition.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/definition/spi/ObjectProjectionDefinition.java
@@ -6,6 +6,7 @@
 
 import java.util.List;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.definition.ProjectionDefinitionContext;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
@@ -45,6 +46,7 @@ public void close() throws Exception {
 		delegate.close();
 	}
 
+	@Deprecated(since = "8.0")
 	@Incubating
 	public static final class SingleValued<T> extends ObjectProjectionDefinition<T, T> {
 		public SingleValued(String fieldPath, CompositeProjectionDefinition<T> delegate) {
@@ -64,8 +66,10 @@ public SearchProjection<T> create(SearchProjectionFactory<?, ?> factory,
 		}
 	}
 
+	@Deprecated(since = "8.0")
 	@Incubating
 	public static final class MultiValued<T> extends ObjectProjectionDefinition<List<T>, T> {
+
 		public MultiValued(String fieldPath, CompositeProjectionDefinition<T> delegate) {
 			super( fieldPath, delegate );
 		}
@@ -79,7 +83,30 @@ protected boolean multi() {
 		public SearchProjection<List<T>> create(SearchProjectionFactory<?, ?> factory,
 				ProjectionDefinitionContext context) {
 			return delegate.apply( factory.withRoot( fieldPath ), factory.object( fieldPath ), context )
-					.multi().toProjection();
+					.collector( ProjectionCollector.list() ).toProjection();
+		}
+	}
+
+	@Incubating
+	public static final class WrappedValued<C, T> extends ObjectProjectionDefinition<C, T> {
+		private final ProjectionCollector.Provider<T, C> collector;
+
+		public WrappedValued(String fieldPath, CompositeProjectionDefinition<T> delegate,
+				ProjectionCollector.Provider<T, C> collector) {
+			super( fieldPath, delegate );
+			this.collector = collector;
+		}
+
+		@Override
+		protected boolean multi() {
+			return !collector.isSingleValued();
+		}
+
+		@Override
+		public SearchProjection<C> create(SearchProjectionFactory<?, ?> factory,
+				ProjectionDefinitionContext context) {
+			return delegate.apply( factory.withRoot( fieldPath ), factory.object( fieldPath ), context )
+					.collector( collector ).toProjection();
 		}
 	}
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/CompositeProjectionValueStep.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/CompositeProjectionValueStep.java
index c1f36407d21..8f5898246e6 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/CompositeProjectionValueStep.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/CompositeProjectionValueStep.java
@@ -4,16 +4,24 @@
  */
 package org.hibernate.search.engine.search.projection.dsl;
 
+import java.util.Comparator;
 import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import java.util.SortedSet;
+
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+import org.hibernate.search.util.common.annotation.Incubating;
 
 /**
  * The step in a composite projection definition
- * where the projection (optionally) can be marked as multi-valued (returning Lists),
+ * where (optionally) the projection collector can be provided, e.g. to mark a projection as multi-valued (returning {@code List}/{@code Set} etc.)
+ * or wrapped in some other container (e.g. {@code Optional<..>}),
  * and where optional parameters can be set.
  * <p>
- * By default (if {@link #multi()} is not called), the projection is single-valued.
+ * By default (if {@link #collector(ProjectionCollector.Provider)} is not called), the projection is single-valued.
  *
- * @param <N> The next step if a method other than {@link #multi()} is called,
+ * @param <N> The next step if a method other than {@link #collector(ProjectionCollector.Provider)} is called,
  * i.e. the return type of methods defined in {@link CompositeProjectionOptionsStep}
  * when called directly on this object.
  * @param <T> The type of composed projections.
@@ -32,7 +40,82 @@ public interface CompositeProjectionValueStep<N extends CompositeProjectionOptio
 	 * is generally not useful: the only effect is that projected values will be wrapped in a one-element {@link List}.
 	 *
 	 * @return A new step to define optional parameters for the projection.
+	 * @deprecated Use {@link #collector(ProjectionCollector.Provider)} instead.
+	 */
+	@Deprecated(since = "8.0")
+	default CompositeProjectionOptionsStep<?, List<T>> multi() {
+		return collector( ProjectionCollector.list() );
+	}
+
+	/**
+	 * Defines how to accumulate composite projection values.
+	 * <p>
+	 * Calling {@code .collector(someMultiValuedCollectorProvider) } is mandatory for multi-valued fields,
+	 * e.g. {@code .collector(ProjectionCollector.list())},
+	 * otherwise the projection will throw an exception upon creating the query.
+	 *
+	 * @param collector The collector provider to apply to this projection.
+	 * @return A new step to define optional parameters for the accumulated projections.
+	 * @param <R> The type of the final result.
+	 */
+	@Incubating
+	<R> CompositeProjectionOptionsStep<?, R> collector(ProjectionCollector.Provider<T, R> collector);
+
+	/**
+	 * Defines the projection as single-valued wrapped in an {@link Optional}, i.e. returning {@code Optional<T>} instead of {@code T}.
+	 *
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default CompositeProjectionOptionsStep<?, Optional<T>> optional() {
+		return collector( ProjectionCollector.optional() );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code List<T>} instead of {@code T}.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default CompositeProjectionOptionsStep<?, List<T>> list() {
+		return collector( ProjectionCollector.list() );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code Set<T>} instead of {@code T}.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default CompositeProjectionOptionsStep<?, Set<T>> set() {
+		return collector( ProjectionCollector.set() );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code SortedSet<T>} instead of {@code T}.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default CompositeProjectionOptionsStep<?, SortedSet<T>> sortedSet() {
+		return collector( ProjectionCollector.sortedSet() );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code SortedSet<T>} instead of {@code T}.
+	 * @param comparator The comparator to use for sorting elements within the set.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default CompositeProjectionOptionsStep<?, SortedSet<T>> sortedSet(Comparator<T> comparator) {
+		return collector( ProjectionCollector.sortedSet( comparator ) );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code T[]} instead of {@code T}.
+	 * @param type The type of array elements.
+	 * @return A new step to define optional parameters.
 	 */
-	CompositeProjectionOptionsStep<?, List<T>> multi();
+	@Incubating
+	default CompositeProjectionOptionsStep<?, T[]> array(Class<T> type) {
+		return collector( ProjectionCollector.array( type ) );
+	}
 
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/DistanceToFieldProjectionValueStep.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/DistanceToFieldProjectionValueStep.java
index 2b889fa130d..34ba0f5adae 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/DistanceToFieldProjectionValueStep.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/DistanceToFieldProjectionValueStep.java
@@ -4,17 +4,25 @@
  */
 package org.hibernate.search.engine.search.projection.dsl;
 
+import java.util.Comparator;
 import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import java.util.SortedSet;
+
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+import org.hibernate.search.util.common.annotation.Incubating;
 
 /**
  * The initial step in a "distance to field" projection definition,
- * where the projection (optionally) can be marked as multi-valued (returning Lists),
+ * where (optionally) the projection collector can be provided, e.g. to mark a projection as multi-valued (returning {@code List}/{@code Set} etc.)
+ * or wrapped in some other container (e.g. {@code Optional<..>}),
  * and where optional parameters can be set.
  * <p>
- * By default (if {@link #multi()} is not called), the projection is considered single-valued,
+ * By default (if {@link #collector(ProjectionCollector.Provider)} is not called), the projection is considered single-valued,
  * and its creation will fail if the field is multi-valued.
  *
- * @param <N> The next step if a method other than {@link #multi()} is called,
+ * @param <N> The next step if a method other than {@link #collector(ProjectionCollector.Provider)} is called,
  * i.e. the return type of methods defined in {@link FieldProjectionOptionsStep}
  * when called directly on this object.
  * @param <T> The type of projected distances.
@@ -29,7 +37,81 @@ public interface DistanceToFieldProjectionValueStep<N extends DistanceToFieldPro
 	 * otherwise the projection will throw an exception upon creating the query.
 	 *
 	 * @return A new step to define optional parameters for the multi-valued projections.
+	 * @deprecated Use {@link #collector(ProjectionCollector.Provider)} instead.
+	 */
+	@Deprecated(since = "8.0")
+	default DistanceToFieldProjectionOptionsStep<?, List<T>> multi() {
+		return collector( ProjectionCollector.list() );
+	}
+
+	/**
+	 * Defines how to accumulate distance projection values.
+	 * <p>
+	 * Calling {@code .collector(someMultiValuedCollectorProvider) } is mandatory for multi-valued fields,
+	 * e.g. {@code .collector(ProjectionCollector.list())},
+	 * otherwise the projection will throw an exception upon creating the query.
+	 *
+	 * @param collector The collector provider to apply to this projection.
+	 * @return A new step to define optional parameters for the accumulated projections.
+	 * @param <R> The type of the final result.
 	 */
-	DistanceToFieldProjectionOptionsStep<?, List<T>> multi();
+	@Incubating
+	<R> DistanceToFieldProjectionOptionsStep<?, R> collector(ProjectionCollector.Provider<T, R> collector);
 
+	/**
+	 * Defines the projection as single-valued wrapped in an {@link Optional}, i.e. returning {@code Optional<T>} instead of {@code T}.
+	 *
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default DistanceToFieldProjectionOptionsStep<?, Optional<T>> optional() {
+		return collector( ProjectionCollector.optional() );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code List<T>} instead of {@code T}.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default DistanceToFieldProjectionOptionsStep<?, List<T>> list() {
+		return collector( ProjectionCollector.list() );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code Set<T>} instead of {@code T}.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default DistanceToFieldProjectionOptionsStep<?, Set<T>> set() {
+		return collector( ProjectionCollector.set() );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code SortedSet<T>} instead of {@code T}.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default DistanceToFieldProjectionOptionsStep<?, SortedSet<T>> sortedSet() {
+		return collector( ProjectionCollector.sortedSet() );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code SortedSet<T>} instead of {@code T}.
+	 * @param comparator The comparator to use for sorting elements within the set.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default DistanceToFieldProjectionOptionsStep<?, SortedSet<T>> sortedSet(Comparator<T> comparator) {
+		return collector( ProjectionCollector.sortedSet( comparator ) );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code T[]} instead of {@code T}.
+	 * @param type The type of array elements.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default DistanceToFieldProjectionOptionsStep<?, T[]> array(Class<T> type) {
+		return collector( ProjectionCollector.array( type ) );
+	}
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/FieldProjectionValueStep.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/FieldProjectionValueStep.java
index d4251c695e7..3b84e67c205 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/FieldProjectionValueStep.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/FieldProjectionValueStep.java
@@ -4,17 +4,25 @@
  */
 package org.hibernate.search.engine.search.projection.dsl;
 
+import java.util.Comparator;
 import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import java.util.SortedSet;
+
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+import org.hibernate.search.util.common.annotation.Incubating;
 
 /**
  * The initial step in a "field" projection definition,
- * where the projection (optionally) can be marked as multi-valued (returning Lists),
+ * where (optionally) the projection collector can be provided, e.g. to mark a projection as multi-valued (returning {@code List}/{@code Set} etc.)
+ * or wrapped in some other container (e.g. {@code Optional<..>}),
  * and where optional parameters can be set.
  * <p>
- * By default (if {@link #multi()} is not called), the projection is considered single-valued,
+ * By default (if {@link #collector(ProjectionCollector.Provider)} is not called), the projection is considered single-valued,
  * and its creation will fail if the field is multi-valued.
  *
- * @param <N> The next step if a method other than {@link #multi()} is called,
+ * @param <N> The next step if a method other than {@link #collector(ProjectionCollector.Provider)} is called,
  * i.e. the return type of methods defined in {@link FieldProjectionOptionsStep}
  * when called directly on this object.
  * @param <T> The type of projected field values.
@@ -29,7 +37,81 @@ public interface FieldProjectionValueStep<N extends FieldProjectionOptionsStep<?
 	 * otherwise the projection will throw an exception upon creating the query.
 	 *
 	 * @return A new step to define optional parameters for the multi-valued projections.
+	 * @deprecated Use {@link #collector(ProjectionCollector.Provider)} instead.
+	 */
+	@Deprecated(since = "8.0")
+	default FieldProjectionOptionsStep<?, List<T>> multi() {
+		return collector( ProjectionCollector.list() );
+	}
+
+	/**
+	 * Defines how to accumulate field projection values.
+	 * <p>
+	 * Calling {@code .collector(someMultiValuedCollectorProvider) } is mandatory for multivalued fields,
+	 * e.g. {@code .collector(ProjectionCollector.list())},
+	 * otherwise the projection will throw an exception upon creating the query.
+	 *
+	 * @param collector The collector provider to apply to this projection.
+	 * @return A new step to define optional parameters for the accumulated projections.
+	 * @param <R> The type of the final result.
 	 */
-	FieldProjectionOptionsStep<?, List<T>> multi();
+	@Incubating
+	<R> FieldProjectionOptionsStep<?, R> collector(ProjectionCollector.Provider<T, R> collector);
 
+	/**
+	 * Defines the projection as single-valued wrapped in an {@link Optional}, i.e. returning {@code Optional<T>} instead of {@code T}.
+	 *
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default FieldProjectionOptionsStep<?, Optional<T>> optional() {
+		return collector( ProjectionCollector.optional() );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code List<T>} instead of {@code T}.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default FieldProjectionOptionsStep<?, List<T>> list() {
+		return collector( ProjectionCollector.list() );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code Set<T>} instead of {@code T}.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default FieldProjectionOptionsStep<?, Set<T>> set() {
+		return collector( ProjectionCollector.set() );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code SortedSet<T>} instead of {@code T}.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default FieldProjectionOptionsStep<?, SortedSet<T>> sortedSet() {
+		return collector( ProjectionCollector.sortedSet() );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code SortedSet<T>} instead of {@code T}.
+	 * @param comparator The comparator to use for sorting elements within the set.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default FieldProjectionOptionsStep<?, SortedSet<T>> sortedSet(Comparator<T> comparator) {
+		return collector( ProjectionCollector.sortedSet( comparator ) );
+	}
+
+	/**
+	 * Defines the projection as multivalued, i.e. returning {@code T[]} instead of {@code T}.
+	 * @param type The type of array elements.
+	 * @return A new step to define optional parameters.
+	 */
+	@Incubating
+	default FieldProjectionOptionsStep<?, T[]> array(Class<T> type) {
+		return collector( ProjectionCollector.array( type ) );
+	}
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/HighlightProjectionOptionsStep.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/HighlightProjectionOptionsStep.java
index d3f3fd97d2d..8e0a25f22a5 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/HighlightProjectionOptionsStep.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/HighlightProjectionOptionsStep.java
@@ -4,9 +4,15 @@
  */
 package org.hibernate.search.engine.search.projection.dsl;
 
+import java.util.Comparator;
+import java.util.Optional;
+import java.util.Set;
+import java.util.SortedSet;
 import java.util.function.Function;
 
 import org.hibernate.search.engine.search.highlighter.dsl.HighlighterOptionsStep;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+import org.hibernate.search.util.common.annotation.Incubating;
 
 /**
  * The initial and final step in a highlight definition, where optional parameters can be set.
@@ -35,7 +41,97 @@ public interface HighlightProjectionOptionsStep extends HighlightProjectionFinal
 	 *
 	 * @return A final step in the highlight projection definition.
 	 * @see HighlighterOptionsStep#numberOfFragments(int)
+	 * @deprecated Use the {@link #collector(ProjectionCollector.Provider)} instead, e.g. {@code .collector(ProjectionCollector.single())}
 	 */
+	@Deprecated(since = "8.0")
 	SingleHighlightProjectionFinalStep single();
 
+	/**
+	 * Defines the collector to apply to the highlighted strings.
+	 * <p>
+	 * By default, highlighting results in a list {@code List<String>} of highlighted strings.
+	 * This method allows changing the returned type to a different collection of strings, e.g. {@code Set<String>}/{@code String[]}
+	 * or obtaining a single-valued projection (i.e. {@code projectionCollectorProvider.isSingleValued () == true}).
+	 * <p>
+	 * Note: single-valued projections can only be used when the highlighter
+	 * that creates highlighted fragments for this projection is configured
+	 * to return a single fragment at most, i.e. when {@link HighlighterOptionsStep#numberOfFragments(int) .numberOfFragments(1)}
+	 * is applied to the highlighter.
+	 * Otherwise, it will lead to an exception being thrown when the query is created.
+	 *
+	 * @param collector The collector provider to apply to this projection.
+	 * @return A final step in the highlight projection definition.
+	 * @param <R> The type of the final result.
+	 */
+	@Incubating
+	<R> ProjectionFinalStep<R> collector(ProjectionCollector.Provider<String, R> collector);
+
+	/**
+	 * Defines the projection as single-valued, i.e. returning {@code String} instead of {@code List<String>}.
+	 * <p>
+	 * Can only be used when the highlighter that creates highlighted fragments for this projection is configured
+	 * to return a single fragment at most, i.e. when {@link HighlighterOptionsStep#numberOfFragments(int) .numberOfFragments(1)}
+	 * is applied to the highlighter.
+	 * Otherwise, it will lead to an exception being thrown when the query is created.
+	 *
+	 * @return A final step in the highlight projection definition.
+	 * @see HighlighterOptionsStep#numberOfFragments(int)
+	 */
+	@Incubating
+	default ProjectionFinalStep<String> nullable() {
+		return collector( ProjectionCollector.nullable() );
+	}
+
+	/**
+	 * Defines the projection as single-valued wrapped in an {@link Optional}, i.e. returning {@code Optional<String>} instead of {@code List<String>}.
+	 * <p>
+	 * Can only be used when the highlighter that creates highlighted fragments for this projection is configured
+	 * to return a single fragment at most, i.e. when {@link HighlighterOptionsStep#numberOfFragments(int) .numberOfFragments(1)}
+	 * is applied to the highlighter.
+	 * Otherwise, it will lead to an exception being thrown when the query is created.
+	 *
+	 * @return A final step in the highlight projection definition.
+	 * @see HighlighterOptionsStep#numberOfFragments(int)
+	 */
+	@Incubating
+	default ProjectionFinalStep<Optional<String>> optional() {
+		return collector( ProjectionCollector.optional() );
+	}
+
+	/**
+	 * Changes the collection accumulating the values to {@link Set} instead of {@link java.util.List}.
+	 * @return A final step in the highlight projection definition.
+	 */
+	@Incubating
+	default ProjectionFinalStep<Set<String>> set() {
+		return collector( ProjectionCollector.set() );
+	}
+
+	/**
+	 * Changes the collection accumulating the values to {@link SortedSet} instead of {@link java.util.List}.
+	 * @return A final step in the highlight projection definition.
+	 */
+	@Incubating
+	default ProjectionFinalStep<SortedSet<String>> sortedSet() {
+		return collector( ProjectionCollector.sortedSet() );
+	}
+
+	/**
+	 * Changes the collection accumulating the values to {@link SortedSet} instead of {@link java.util.List}.
+	 * @param comparator The comparator to use for sorting strings within the set.
+	 * @return A final step in the highlight projection definition.
+	 */
+	@Incubating
+	default ProjectionFinalStep<SortedSet<String>> sortedSet(Comparator<String> comparator) {
+		return collector( ProjectionCollector.sortedSet( comparator ) );
+	}
+
+	/**
+	 * Changes the collection accumulating the values to {@code String[]} instead of {@link java.util.List}.
+	 * @return A final step in the highlight projection definition.
+	 */
+	@Incubating
+	default ProjectionFinalStep<String[]> array() {
+		return collector( ProjectionCollector.array( String.class ) );
+	}
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/SearchProjectionFactory.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/SearchProjectionFactory.java
index 91b6752c7f9..1fef0644846 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/SearchProjectionFactory.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/SearchProjectionFactory.java
@@ -12,6 +12,7 @@
 import org.hibernate.search.engine.common.EntityReference;
 import org.hibernate.search.engine.search.common.NamedValues;
 import org.hibernate.search.engine.search.common.ValueModel;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.spatial.GeoPoint;
 import org.hibernate.search.util.common.SearchException;
@@ -217,7 +218,7 @@ default FieldProjectionValueStep<?, Object> field(String fieldPath,
 	 * Compared to the basic {@link #composite() composite projection},
 	 * an object projection is bound to a specific object field,
 	 * and thus it yields zero, one or many values, as many as there are objects in the targeted object field.
-	 * Therefore, you must take care of calling {@link CompositeProjectionValueStep#multi()}
+	 * Therefore, you must take care of calling {@link CompositeProjectionValueStep#collector(ProjectionCollector.Provider)}
 	 * if the object field is multi-valued.
 	 *
 	 * @param objectFieldPath The <a href="#field-paths">path</a> to the object field whose object(s) will be extracted.
@@ -232,7 +233,7 @@ default FieldProjectionValueStep<?, Object> field(String fieldPath,
 	 * On contrary to the {@link #object(String)  object projection},
 	 * a composite projection is not bound to a specific object field,
 	 * and thus it will always yield one and only one value,
-	 * regardless of whether {@link CompositeProjectionValueStep#multi()} is called.
+	 * regardless of whether {@link CompositeProjectionValueStep#collector(ProjectionCollector.Provider)} is called.
 	 *
 	 * @return A DSL step where the "composite" projection can be defined in more details.
 	 */
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/CompositeProjectionOptionsStepImpl.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/CompositeProjectionOptionsStepImpl.java
index 2694ffb7bc2..764bba1dcee 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/CompositeProjectionOptionsStepImpl.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/CompositeProjectionOptionsStepImpl.java
@@ -4,10 +4,10 @@
  */
 package org.hibernate.search.engine.search.projection.dsl.impl;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.dsl.CompositeProjectionOptionsStep;
 import org.hibernate.search.engine.search.projection.spi.CompositeProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionCompositor;
 
 public class CompositeProjectionOptionsStepImpl<T, P>
@@ -16,19 +16,19 @@ public class CompositeProjectionOptionsStepImpl<T, P>
 	final CompositeProjectionBuilder builder;
 	final SearchProjection<?>[] inners;
 	final ProjectionCompositor<?, T> compositor;
-	private final ProjectionAccumulator.Provider<T, P> accumulatorProvider;
+	private final ProjectionCollector.Provider<T, P> collectorProvider;
 
 	public CompositeProjectionOptionsStepImpl(CompositeProjectionBuilder builder,
 			SearchProjection<?>[] inners, ProjectionCompositor<?, T> compositor,
-			ProjectionAccumulator.Provider<T, P> accumulatorProvider) {
+			ProjectionCollector.Provider<T, P> collectorProvider) {
 		this.builder = builder;
 		this.inners = inners;
 		this.compositor = compositor;
-		this.accumulatorProvider = accumulatorProvider;
+		this.collectorProvider = collectorProvider;
 	}
 
 	@Override
 	public SearchProjection<P> toProjection() {
-		return builder.build( inners, compositor, accumulatorProvider );
+		return builder.build( inners, compositor, collectorProvider );
 	}
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/CompositeProjectionValueStepImpl.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/CompositeProjectionValueStepImpl.java
index 3cd4f9741a7..3be534ad2fb 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/CompositeProjectionValueStepImpl.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/CompositeProjectionValueStepImpl.java
@@ -4,13 +4,11 @@
  */
 package org.hibernate.search.engine.search.projection.dsl.impl;
 
-import java.util.List;
-
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.dsl.CompositeProjectionOptionsStep;
 import org.hibernate.search.engine.search.projection.dsl.CompositeProjectionValueStep;
 import org.hibernate.search.engine.search.projection.spi.CompositeProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionCompositor;
 
 public class CompositeProjectionValueStepImpl<T>
@@ -19,12 +17,11 @@ public class CompositeProjectionValueStepImpl<T>
 
 	public CompositeProjectionValueStepImpl(CompositeProjectionBuilder builder,
 			SearchProjection<?>[] inners, ProjectionCompositor<?, T> compositor) {
-		super( builder, inners, compositor, ProjectionAccumulator.single() );
+		super( builder, inners, compositor, ProjectionCollector.nullable() );
 	}
 
 	@Override
-	public CompositeProjectionOptionsStep<?, List<T>> multi() {
-		return new CompositeProjectionOptionsStepImpl<>( builder, inners, compositor,
-				ProjectionAccumulator.list() );
+	public <R> CompositeProjectionOptionsStep<?, R> collector(ProjectionCollector.Provider<T, R> collector) {
+		return new CompositeProjectionOptionsStepImpl<>( builder, inners, compositor, collector );
 	}
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/DistanceToFieldProjectionOptionsStepImpl.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/DistanceToFieldProjectionOptionsStepImpl.java
index e5a94c343c4..3cea9dd1e75 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/DistanceToFieldProjectionOptionsStepImpl.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/DistanceToFieldProjectionOptionsStepImpl.java
@@ -4,10 +4,10 @@
  */
 package org.hibernate.search.engine.search.projection.dsl.impl;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.dsl.DistanceToFieldProjectionOptionsStep;
 import org.hibernate.search.engine.search.projection.spi.DistanceToFieldProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.spatial.DistanceUnit;
 import org.hibernate.search.util.common.impl.Contracts;
 
@@ -15,12 +15,12 @@ public class DistanceToFieldProjectionOptionsStepImpl<P>
 		implements DistanceToFieldProjectionOptionsStep<DistanceToFieldProjectionOptionsStepImpl<P>, P> {
 
 	protected final DistanceToFieldProjectionBuilder distanceFieldProjectionBuilder;
-	private final ProjectionAccumulator.Provider<Double, P> accumulatorProvider;
+	private final ProjectionCollector.Provider<Double, P> collectorProvider;
 
 	DistanceToFieldProjectionOptionsStepImpl(DistanceToFieldProjectionBuilder distanceFieldProjectionBuilder,
-			ProjectionAccumulator.Provider<Double, P> accumulatorProvider) {
+			ProjectionCollector.Provider<Double, P> collectorProvider) {
 		this.distanceFieldProjectionBuilder = distanceFieldProjectionBuilder;
-		this.accumulatorProvider = accumulatorProvider;
+		this.collectorProvider = collectorProvider;
 	}
 
 	@Override
@@ -33,7 +33,7 @@ public DistanceToFieldProjectionOptionsStepImpl<P> unit(DistanceUnit unit) {
 
 	@Override
 	public SearchProjection<P> toProjection() {
-		return distanceFieldProjectionBuilder.build( accumulatorProvider );
+		return distanceFieldProjectionBuilder.build( collectorProvider );
 	}
 
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/DistanceToFieldProjectionValueStepImpl.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/DistanceToFieldProjectionValueStepImpl.java
index 9c739097e24..26e1a5e4d11 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/DistanceToFieldProjectionValueStepImpl.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/DistanceToFieldProjectionValueStepImpl.java
@@ -4,12 +4,10 @@
  */
 package org.hibernate.search.engine.search.projection.dsl.impl;
 
-import java.util.List;
-
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.dsl.DistanceToFieldProjectionOptionsStep;
 import org.hibernate.search.engine.search.projection.dsl.DistanceToFieldProjectionValueStep;
 import org.hibernate.search.engine.search.projection.dsl.spi.SearchProjectionDslContext;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionTypeKeys;
 import org.hibernate.search.engine.spatial.GeoPoint;
 
@@ -20,14 +18,15 @@ public final class DistanceToFieldProjectionValueStepImpl
 	public DistanceToFieldProjectionValueStepImpl(SearchProjectionDslContext<?> dslContext, String fieldPath,
 			GeoPoint center) {
 		super( dslContext.scope().fieldQueryElement( fieldPath, ProjectionTypeKeys.DISTANCE ),
-				ProjectionAccumulator.single() );
+				ProjectionCollector.nullable() );
 		distanceFieldProjectionBuilder.center( center );
 	}
 
 	@Override
-	public DistanceToFieldProjectionOptionsStep<?, List<Double>> multi() {
+	public <R> DistanceToFieldProjectionOptionsStep<?, R> collector(ProjectionCollector.Provider<Double, R> collector) {
 		return new DistanceToFieldProjectionOptionsStepImpl<>( distanceFieldProjectionBuilder,
-				ProjectionAccumulator.list() );
+				collector
+		);
 	}
 
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/FieldProjectionOptionsStepImpl.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/FieldProjectionOptionsStepImpl.java
index 0c56aeb6483..95b020b8dd3 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/FieldProjectionOptionsStepImpl.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/FieldProjectionOptionsStepImpl.java
@@ -4,26 +4,26 @@
  */
 package org.hibernate.search.engine.search.projection.dsl.impl;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.dsl.FieldProjectionOptionsStep;
 import org.hibernate.search.engine.search.projection.spi.FieldProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 
 public class FieldProjectionOptionsStepImpl<T, P>
 		implements FieldProjectionOptionsStep<FieldProjectionOptionsStepImpl<T, P>, P> {
 
 	protected final FieldProjectionBuilder<T> fieldProjectionBuilder;
-	private final ProjectionAccumulator.Provider<T, P> accumulatorProvider;
+	private final ProjectionCollector.Provider<T, P> collectorProvider;
 
 	FieldProjectionOptionsStepImpl(FieldProjectionBuilder<T> fieldProjectionBuilder,
-			ProjectionAccumulator.Provider<T, P> accumulatorProvider) {
+			ProjectionCollector.Provider<T, P> collectorProvider) {
 		this.fieldProjectionBuilder = fieldProjectionBuilder;
-		this.accumulatorProvider = accumulatorProvider;
+		this.collectorProvider = collectorProvider;
 	}
 
 	@Override
 	public SearchProjection<P> toProjection() {
-		return fieldProjectionBuilder.build( accumulatorProvider );
+		return fieldProjectionBuilder.build( collectorProvider );
 	}
 
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/FieldProjectionValueStepImpl.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/FieldProjectionValueStepImpl.java
index 0732dc56bda..24605d0d583 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/FieldProjectionValueStepImpl.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/FieldProjectionValueStepImpl.java
@@ -4,14 +4,12 @@
  */
 package org.hibernate.search.engine.search.projection.dsl.impl;
 
-import java.util.List;
-
 import org.hibernate.search.engine.search.common.ValueModel;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.dsl.FieldProjectionOptionsStep;
 import org.hibernate.search.engine.search.projection.dsl.FieldProjectionValueStep;
 import org.hibernate.search.engine.search.projection.dsl.spi.SearchProjectionDslContext;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionTypeKeys;
 
 public final class FieldProjectionValueStepImpl<T>
@@ -22,12 +20,12 @@ public FieldProjectionValueStepImpl(SearchProjectionDslContext<?> dslContext, St
 			Class<T> clazz, ValueModel valueModel) {
 		super( dslContext.scope().fieldQueryElement( fieldPath, ProjectionTypeKeys.FIELD )
 				.type( clazz, valueModel ),
-				ProjectionAccumulator.single() );
+				ProjectionCollector.nullable() );
 	}
 
 	@Override
-	public FieldProjectionOptionsStep<?, List<T>> multi() {
-		return new FieldProjectionOptionsStepImpl<>( fieldProjectionBuilder, ProjectionAccumulator.list() );
+	public <R> FieldProjectionOptionsStep<?, R> collector(ProjectionCollector.Provider<T, R> collector) {
+		return new FieldProjectionOptionsStepImpl<>( fieldProjectionBuilder, collector );
 	}
 
 	@Override
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/HighlightProjectionOptionsStepImpl.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/HighlightProjectionOptionsStepImpl.java
index 6e01893b1f8..0122d728a1e 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/HighlightProjectionOptionsStepImpl.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/impl/HighlightProjectionOptionsStepImpl.java
@@ -6,13 +6,14 @@
 
 import java.util.List;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.dsl.HighlightProjectionFinalStep;
 import org.hibernate.search.engine.search.projection.dsl.HighlightProjectionOptionsStep;
+import org.hibernate.search.engine.search.projection.dsl.ProjectionFinalStep;
 import org.hibernate.search.engine.search.projection.dsl.SingleHighlightProjectionFinalStep;
 import org.hibernate.search.engine.search.projection.dsl.spi.HighlightProjectionBuilder;
 import org.hibernate.search.engine.search.projection.dsl.spi.SearchProjectionDslContext;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionTypeKeys;
 
 public class HighlightProjectionOptionsStepImpl
@@ -31,21 +32,40 @@ public HighlightProjectionOptionsStep highlighter(String highlighterName) {
 		return this;
 	}
 
+	@SuppressWarnings("deprecation")
 	@Override
 	public SingleHighlightProjectionFinalStep single() {
 		return new SingleHighlightProjectionFinalStepImpl();
 	}
 
+	@Override
+	public <R> ProjectionFinalStep<R> collector(
+			ProjectionCollector.Provider<String, R> collector) {
+		return new CollectorHighlightProjectionFinalStepImpl<>( collector );
+	}
+
 	@Override
 	public SearchProjection<List<String>> toProjection() {
-		return highlight.build( ProjectionAccumulator.list() );
+		return highlight.build( ProjectionCollector.list() );
 	}
 
-	private class SingleHighlightProjectionFinalStepImpl implements SingleHighlightProjectionFinalStep {
-		@Override
-		public SearchProjection<String> toProjection() {
-			return highlight.build( ProjectionAccumulator.single() );
+	private class SingleHighlightProjectionFinalStepImpl extends CollectorHighlightProjectionFinalStepImpl<String>
+			implements SingleHighlightProjectionFinalStep {
+		public SingleHighlightProjectionFinalStepImpl() {
+			super( ProjectionCollector.nullable() );
+		}
+	}
+
+	private class CollectorHighlightProjectionFinalStepImpl<V> implements ProjectionFinalStep<V> {
+		private final ProjectionCollector.Provider<String, V> collectorProvider;
+
+		private CollectorHighlightProjectionFinalStepImpl(ProjectionCollector.Provider<String, V> collectorProvider) {
+			this.collectorProvider = collectorProvider;
 		}
 
+		@Override
+		public SearchProjection<V> toProjection() {
+			return highlight.build( collectorProvider );
+		}
 	}
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/spi/HighlightProjectionBuilder.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/spi/HighlightProjectionBuilder.java
index 1fc0dd1995e..2d0c9b0d905 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/spi/HighlightProjectionBuilder.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/dsl/spi/HighlightProjectionBuilder.java
@@ -4,8 +4,8 @@
  */
 package org.hibernate.search.engine.search.projection.dsl.spi;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 
 public abstract class HighlightProjectionBuilder {
 	protected final String path;
@@ -20,5 +20,5 @@ public HighlightProjectionBuilder highlighter(String highlighterName) {
 		return this;
 	}
 
-	public abstract <V> SearchProjection<V> build(ProjectionAccumulator.Provider<String, V> accumulatorProvider);
+	public abstract <V> SearchProjection<V> build(ProjectionCollector.Provider<String, V> collectorProvider);
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ArrayProjectionCollector.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ArrayProjectionCollector.java
new file mode 100644
index 00000000000..17de6a669c3
--- /dev/null
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ArrayProjectionCollector.java
@@ -0,0 +1,59 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.engine.search.projection.spi;
+
+import java.lang.reflect.Array;
+import java.util.List;
+
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+
+/**
+ * A {@link ProjectionCollector} that can accumulate any number of values into a {@code V[]}.
+ *
+ * @param <E> The type of extracted values to accumulate before being transformed.
+ * @param <V> The type of values to accumulate obtained by transforming extracted values ({@code E}).
+ */
+final class ArrayProjectionCollector<E, V> extends ListBasedProjectionCollector<E, V, V[]> {
+
+	static <U, R> Provider<U, R> provider(Class<? super U> elementType) {
+		return new ArrayProvider<>( elementType );
+	}
+
+	private ArrayProjectionCollector(Class<? super V> elementType) {
+		this.elementType = elementType;
+	}
+
+	private final Class<? super V> elementType;
+
+	@SuppressWarnings("unchecked")
+	@Override
+	public V[] doFinish(List<V> accumulated) {
+		V[] array = (V[]) Array.newInstance( elementType, accumulated.size() );
+		int i = 0;
+		for ( V v : accumulated ) {
+			array[i++] = v;
+		}
+		return array;
+	}
+
+	@SuppressWarnings("unchecked")
+	private static class ArrayProvider<U, R> implements Provider<U, R> {
+		private final ArrayProjectionCollector<?, U> instance;
+
+		private ArrayProvider(Class<? super U> elementType) {
+			instance = new ArrayProjectionCollector<>( elementType );
+		}
+
+		@Override
+		public <T> ProjectionCollector<T, U, ?, R> get() {
+			return (ProjectionCollector<T, U, ?, R>) instance;
+		}
+
+		@Override
+		public boolean isSingleValued() {
+			return false;
+		}
+	}
+}
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/BaseSingleValuedProjectionCollector.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/BaseSingleValuedProjectionCollector.java
new file mode 100644
index 00000000000..684e8c272f3
--- /dev/null
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/BaseSingleValuedProjectionCollector.java
@@ -0,0 +1,72 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.engine.search.projection.spi;
+
+import java.lang.invoke.MethodHandles;
+
+import org.hibernate.search.engine.backend.types.converter.FromDocumentValueConverter;
+import org.hibernate.search.engine.backend.types.converter.runtime.FromDocumentValueConvertContext;
+import org.hibernate.search.engine.logging.impl.Log;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+import org.hibernate.search.util.common.logging.impl.LoggerFactory;
+
+/**
+ * A {@link ProjectionCollector} that can accumulate up to one value, and will throw an exception beyond that.
+ *
+ * @param <E> The type of extracted values to accumulate before being transformed.
+ * @param <V> The type of values to accumulate obtained by transforming extracted values ({@code E}).
+ */
+abstract class BaseSingleValuedProjectionCollector<E, V, R>
+		implements ProjectionCollector<E, V, Object, R> {
+
+	private static final Log log = LoggerFactory.make( Log.class, MethodHandles.lookup() );
+
+	protected BaseSingleValuedProjectionCollector() {
+	}
+
+	@Override
+	public final String toString() {
+		return getClass().getSimpleName();
+	}
+
+	@Override
+	public final E createInitial() {
+		return null;
+	}
+
+	@Override
+	public final E accumulate(Object accumulated, E value) {
+		if ( accumulated != null ) {
+			throw log.unexpectedMultiValuedField( accumulated, value );
+		}
+		return value;
+	}
+
+	@Override
+	public final int size(Object accumulated) {
+		return accumulated == null ? 0 : 1;
+	}
+
+	@Override
+	@SuppressWarnings("unchecked")
+	public final E get(Object accumulated, int index) {
+		return (E) accumulated;
+	}
+
+	@Override
+	public final Object transform(Object accumulated, int index, V transformed) {
+		if ( index != 0 ) {
+			throw new IndexOutOfBoundsException( "Invalid index passed to " + this + ": " + index );
+		}
+		return transformed;
+	}
+
+	@Override
+	@SuppressWarnings("unchecked")
+	public final Object transformAll(Object accumulated, FromDocumentValueConverter<? super E, ? extends V> converter,
+			FromDocumentValueConvertContext context) {
+		return converter.fromDocumentValue( (E) accumulated, context );
+	}
+}
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/BuiltInProjectionCollectors.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/BuiltInProjectionCollectors.java
new file mode 100644
index 00000000000..24af64dbdb3
--- /dev/null
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/BuiltInProjectionCollectors.java
@@ -0,0 +1,60 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.engine.search.projection.spi;
+
+import java.util.Comparator;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import java.util.SortedSet;
+import java.util.function.Function;
+
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+
+/**
+ * Provides access to built-in projection collectors.
+ */
+public interface BuiltInProjectionCollectors {
+
+	@SuppressWarnings("unchecked") // PROVIDER works for any V.
+	static <V> ProjectionCollector.Provider<V, V> nullable() {
+		return SingleValuedProjectionAccumulator.PROVIDER;
+	}
+
+	@SuppressWarnings("unchecked") // PROVIDER works for any V.
+	static <V> ProjectionCollector.Provider<V, List<V>> list() {
+		return ListProjectionAccumulator.PROVIDER;
+	}
+
+	static <V, C> ProjectionCollector.Provider<V, C> simple(
+			Function<List<V>, C> converter) {
+		return new SimpleProjectionCollector.Provider<>( converter );
+	}
+
+	static <V> ProjectionCollector.Provider<V, V[]> array(
+			Class<? super V> componentType) {
+		return ArrayProjectionCollector.provider( componentType );
+	}
+
+	@SuppressWarnings("unchecked") // PROVIDER works for any V.
+	static <V> ProjectionCollector.Provider<V, Set<V>> set() {
+		return SetProjectionCollector.PROVIDER;
+	}
+
+	@SuppressWarnings("unchecked") // PROVIDER works for any V.
+	static <V> ProjectionCollector.Provider<V, SortedSet<V>> sortedSet() {
+		return SortedSetProjectionCollector.PROVIDER;
+	}
+
+	static <V> ProjectionCollector.Provider<V, SortedSet<V>> sortedSet(
+			Comparator<? super V> comparator) {
+		return SortedSetComparatorProjectionCollector.provider( comparator );
+	}
+
+	@SuppressWarnings("unchecked") // PROVIDER works for any V.
+	static <V> ProjectionCollector.Provider<V, Optional<V>> optional() {
+		return OptionalProjectionCollector.PROVIDER;
+	}
+}
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/CompositeProjectionBuilder.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/CompositeProjectionBuilder.java
index 5365ca5d765..d3d54041ca0 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/CompositeProjectionBuilder.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/CompositeProjectionBuilder.java
@@ -4,11 +4,12 @@
  */
 package org.hibernate.search.engine.search.projection.spi;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 
 public interface CompositeProjectionBuilder {
 
 	<E, V, P> SearchProjection<P> build(SearchProjection<?>[] inners, ProjectionCompositor<E, V> compositor,
-			ProjectionAccumulator.Provider<V, P> accumulatorProvider);
+			ProjectionCollector.Provider<V, P> collectorProvider);
 
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/DistanceToFieldProjectionBuilder.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/DistanceToFieldProjectionBuilder.java
index 3df387d47ae..ed0d44009e9 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/DistanceToFieldProjectionBuilder.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/DistanceToFieldProjectionBuilder.java
@@ -4,6 +4,7 @@
  */
 package org.hibernate.search.engine.search.projection.spi;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.spatial.DistanceUnit;
 import org.hibernate.search.engine.spatial.GeoPoint;
@@ -16,9 +17,9 @@ public interface DistanceToFieldProjectionBuilder extends SearchProjectionBuilde
 
 	@Override
 	default SearchProjection<Double> build() {
-		return build( ProjectionAccumulator.single() );
+		return build( ProjectionCollector.nullable() );
 	}
 
-	<P> SearchProjection<P> build(ProjectionAccumulator.Provider<Double, P> accumulatorProvider);
+	<P> SearchProjection<P> build(ProjectionCollector.Provider<Double, P> collectorProvider);
 
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/FieldProjectionBuilder.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/FieldProjectionBuilder.java
index 3ffcd725fb6..0d18fbc1abe 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/FieldProjectionBuilder.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/FieldProjectionBuilder.java
@@ -5,6 +5,7 @@
 package org.hibernate.search.engine.search.projection.spi;
 
 import org.hibernate.search.engine.search.common.ValueModel;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 
 public interface FieldProjectionBuilder<T> extends SearchProjectionBuilder<T> {
@@ -15,9 +16,9 @@ interface TypeSelector {
 
 	@Override
 	default SearchProjection<T> build() {
-		return build( ProjectionAccumulator.single() );
+		return build( ProjectionCollector.nullable() );
 	}
 
-	<P> SearchProjection<P> build(ProjectionAccumulator.Provider<T, P> accumulatorProvider);
+	<P> SearchProjection<P> build(ProjectionCollector.Provider<T, P> collectorProvider);
 
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ListBasedProjectionCollector.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ListBasedProjectionCollector.java
new file mode 100644
index 00000000000..2e9c14a1950
--- /dev/null
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ListBasedProjectionCollector.java
@@ -0,0 +1,77 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.engine.search.projection.spi;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+
+/**
+ * A {@link ProjectionCollector} that can accumulate any number of values into a {@link List},
+ * and transforms that list into an arbitrary container on {@link #finish(List)}.
+ *
+ * @param <E> The type of extracted values to accumulate before being transformed.
+ * @param <V> The type of values to accumulate obtained by transforming extracted values ({@code E}).
+ * @param <R> The type of the final result containing values of type {@code V}.
+ */
+@SuppressWarnings("deprecation")
+abstract class ListBasedProjectionCollector<E, V, R>
+		implements ProjectionCollector<E, V, List<Object>, R> {
+
+	ListBasedProjectionCollector() {
+	}
+
+	@Override
+	public final String toString() {
+		return getClass().getSimpleName();
+	}
+
+	@Override
+	public final List<Object> createInitial() {
+		return new ArrayList<>();
+	}
+
+	@Override
+	public final List<Object> accumulate(List<Object> accumulated, E value) {
+		accumulated.add( value );
+		return accumulated;
+	}
+
+	@Override
+	public final List<Object> accumulateAll(List<Object> accumulated, Collection<E> values) {
+		accumulated.addAll( values );
+		return accumulated;
+	}
+
+	@Override
+	public final int size(List<Object> accumulated) {
+		return accumulated.size();
+	}
+
+	@Override
+	@SuppressWarnings("unchecked")
+	public final E get(List<Object> accumulated, int index) {
+		return (E) accumulated.get( index );
+	}
+
+	@Override
+	public final List<Object> transform(List<Object> accumulated, int index, V transformed) {
+		accumulated.set( index, transformed );
+		return accumulated;
+	}
+
+	@Override
+	@SuppressWarnings({ "unchecked", "rawtypes" })
+	public final R finish(List<Object> accumulated) {
+		// Hack to avoid instantiating another list: we convert a List<Object> into a List<U> just by replacing its elements.
+		// It works *only* because we know the actual underlying type of the list,
+		// and we know it can work just as well with U as with Object.
+		return doFinish( (List<V>) (List) accumulated );
+	}
+
+	protected abstract R doFinish(List<V> accumulated);
+}
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ListProjectionAccumulator.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ListProjectionAccumulator.java
index cd21f4ef49a..3cfc0bf6f8b 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ListProjectionAccumulator.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ListProjectionAccumulator.java
@@ -4,20 +4,22 @@
  */
 package org.hibernate.search.engine.search.projection.spi;
 
-import java.util.ArrayList;
-import java.util.Collection;
 import java.util.List;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+
 /**
- * A {@link ProjectionAccumulator} that can accumulate any number of values into a {@link java.util.List}.
+ * A {@link ProjectionCollector} that can accumulate any number of values into a {@link java.util.List}.
  *
  * @param <E> The type of extracted values to accumulate before being transformed.
  * @param <V> The type of values to accumulate obtained by transforming extracted values ({@code E}).
  */
-final class ListProjectionAccumulator<E, V> implements ProjectionAccumulator<E, V, List<Object>, List<V>> {
+@SuppressWarnings("deprecation")
+final class ListProjectionAccumulator<E, V> extends ListBasedProjectionCollector<E, V, List<V>>
+		implements ProjectionAccumulator<E, V, List<Object>, List<V>> {
 
 	@SuppressWarnings("rawtypes")
-	static final Provider PROVIDER = new Provider() {
+	static final ProjectionAccumulator.Provider PROVIDER = new ProjectionAccumulator.Provider() {
 		private final ListProjectionAccumulator instance = new ListProjectionAccumulator();
 
 		@Override
@@ -35,50 +37,7 @@ private ListProjectionAccumulator() {
 	}
 
 	@Override
-	public String toString() {
-		return getClass().getSimpleName();
-	}
-
-	@Override
-	public List<Object> createInitial() {
-		return new ArrayList<>();
-	}
-
-	@Override
-	public List<Object> accumulate(List<Object> accumulated, E value) {
-		accumulated.add( value );
-		return accumulated;
-	}
-
-	@Override
-	public List<Object> accumulateAll(List<Object> accumulated, Collection<E> values) {
-		accumulated.addAll( values );
-		return accumulated;
-	}
-
-	@Override
-	public int size(List<Object> accumulated) {
-		return accumulated.size();
-	}
-
-	@Override
-	@SuppressWarnings("unchecked")
-	public E get(List<Object> accumulated, int index) {
-		return (E) accumulated.get( index );
-	}
-
-	@Override
-	public List<Object> transform(List<Object> accumulated, int index, V transformed) {
-		accumulated.set( index, transformed );
+	public List<V> doFinish(List<V> accumulated) {
 		return accumulated;
 	}
-
-	@Override
-	@SuppressWarnings({ "unchecked", "rawtypes" })
-	public List<V> finish(List<Object> accumulated) {
-		// Hack to avoid instantiating another list: we convert a List<Object> into a List<U> just by replacing its elements.
-		// It works *only* because we know the actual underlying type of the list,
-		// and we know it can work just as well with U as with Object.
-		return (List<V>) (List) accumulated;
-	}
 }
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/OptionalProjectionCollector.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/OptionalProjectionCollector.java
new file mode 100644
index 00000000000..8db24265fe8
--- /dev/null
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/OptionalProjectionCollector.java
@@ -0,0 +1,43 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.engine.search.projection.spi;
+
+import java.util.Optional;
+
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+
+/**
+ * A {@link ProjectionCollector} that can accumulate up to one value, and will throw an exception beyond that.
+ * The value is wrapped in an {@link Optional}.
+ *
+ * @param <E> The type of extracted values to accumulate before being transformed.
+ * @param <V> The type of values to accumulate obtained by transforming extracted values ({@code E}).
+ */
+final class OptionalProjectionCollector<E, V> extends BaseSingleValuedProjectionCollector<E, V, Optional<V>> {
+
+	@SuppressWarnings("rawtypes")
+	static final Provider PROVIDER = new Provider() {
+		private final OptionalProjectionCollector instance = new OptionalProjectionCollector();
+
+		@Override
+		public ProjectionCollector get() {
+			return instance;
+		}
+
+		@Override
+		public boolean isSingleValued() {
+			return true;
+		}
+	};
+
+	private OptionalProjectionCollector() {
+	}
+
+	@Override
+	@SuppressWarnings("unchecked")
+	public Optional<V> finish(Object accumulated) {
+		return Optional.ofNullable( (V) accumulated );
+	}
+}
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ProjectionAccumulator.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ProjectionAccumulator.java
index d90e5a44632..8a380a9367a 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ProjectionAccumulator.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/ProjectionAccumulator.java
@@ -9,6 +9,7 @@
 
 import org.hibernate.search.engine.backend.types.converter.runtime.FromDocumentValueConvertContext;
 import org.hibernate.search.engine.backend.types.converter.spi.ProjectionConverter;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 
 /**
  * A variation on {@link java.util.stream.Collector} suitable for projections on field values.
@@ -30,11 +31,15 @@
  * @param <A> The type of the temporary storage for accumulated values,
  * before and after being transformed.
  * @param <R> The type of the final result containing values of type {@code V}.
+ *
+ * @deprecated Use {@link ProjectionCollector} instead.
  */
-public interface ProjectionAccumulator<E, V, A, R> {
+@Deprecated(since = "8.0")
+public interface ProjectionAccumulator<E, V, A, R>
+		extends ProjectionCollector<E, V, A, R> {
 
 	@SuppressWarnings("unchecked") // PROVIDER works for any V.
-	static <V> ProjectionAccumulator.Provider<V, V> single() {
+	static <V> Provider<V, V> single() {
 		return SingleValuedProjectionAccumulator.PROVIDER;
 	}
 
@@ -51,6 +56,7 @@ static <V> Provider<V, List<V>> list() {
 	 * @return The initial accumulated container,
 	 * to pass to the first call to {@link #accumulate(Object, Object)}.
 	 */
+	@Override
 	A createInitial();
 
 	/**
@@ -64,6 +70,7 @@ static <V> Provider<V, List<V>> list() {
 	 * @param value The value to accumulate.
 	 * @return The new accumulated value.
 	 */
+	@Override
 	A accumulate(A accumulated, E value);
 
 	/**
@@ -77,6 +84,7 @@ static <V> Provider<V, List<V>> list() {
 	 * @param values The values to accumulate.
 	 * @return The new accumulated value.
 	 */
+	@Override
 	default A accumulateAll(A accumulated, Collection<E> values) {
 		for ( E value : values ) {
 			accumulated = accumulate( accumulated, value );
@@ -89,6 +97,7 @@ default A accumulateAll(A accumulated, Collection<E> values) {
 	 * returned by the last call to {@link #accumulate(Object, Object)}.
 	 * @return The number of elements in the accumulated value.
 	 */
+	@Override
 	int size(A accumulated);
 
 	/**
@@ -101,6 +110,7 @@ default A accumulateAll(A accumulated, Collection<E> values) {
 	 * @param index The index of the value to retrieve.
 	 * @return The value at the given index.
 	 */
+	@Override
 	E get(A accumulated, int index);
 
 	/**
@@ -115,6 +125,7 @@ default A accumulateAll(A accumulated, Collection<E> values) {
 	 * @param transformed The transformed value.
 	 * @return The new accumulated value.
 	 */
+	@Override
 	A transform(A accumulated, int index, V transformed);
 
 	/**
@@ -130,12 +141,7 @@ default A accumulateAll(A accumulated, Collection<E> values) {
 	 */
 	default A transformAll(A accumulated, ProjectionConverter<? super E, ? extends V> converter,
 			FromDocumentValueConvertContext context) {
-		for ( int i = 0; i < size( accumulated ); i++ ) {
-			E initial = get( accumulated, i );
-			V transformed = converter.fromDocumentValue( initial, context );
-			accumulated = transform( accumulated, i, transformed );
-		}
-		return accumulated;
+		return transformAll( accumulated, converter.delegate(), context );
 	}
 
 	/**
@@ -149,6 +155,7 @@ default A transformAll(A accumulated, ProjectionConverter<? super E, ? extends V
 	 * or by successive calls to {@link #transform(Object, int, Object)}.
 	 * @return The final result of the accumulation.
 	 */
+	@Override
 	R finish(A accumulated);
 
 	/**
@@ -160,17 +167,19 @@ default A transformAll(A accumulated, ProjectionConverter<? super E, ? extends V
 	 * @param <U> The type of values to accumulate after being transformed.
 	 * @param <R> The type of the final result containing values of type {@code V}.
 	 */
-	interface Provider<U, R> {
+	interface Provider<U, R> extends ProjectionCollector.Provider<U, R> {
 		/**
 		 * @param <T> The type of values to accumulate before being transformed.
 		 * @return An accumulator for the given type.
 		 */
+		@Override
 		<T> ProjectionAccumulator<T, U, ?, R> get();
 
 		/**
 		 * @return {@code true} if accumulators returned by {@link #get()} can only accept a single value,
 		 * and will fail beyond that.
 		 */
+		@Override
 		boolean isSingleValued();
 	}
 
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SetProjectionCollector.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SetProjectionCollector.java
new file mode 100644
index 00000000000..9ddf96ff002
--- /dev/null
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SetProjectionCollector.java
@@ -0,0 +1,43 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.engine.search.projection.spi;
+
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+
+/**
+ * A {@link ProjectionCollector} that can accumulate any number of values into a {@link Set}.
+ *
+ * @param <E> The type of extracted values to accumulate before being transformed.
+ * @param <V> The type of values to accumulate obtained by transforming extracted values ({@code E}).
+ */
+final class SetProjectionCollector<E, V> extends ListBasedProjectionCollector<E, V, Set<V>> {
+
+	@SuppressWarnings("rawtypes")
+	static final Provider PROVIDER = new Provider() {
+		private final SetProjectionCollector instance = new SetProjectionCollector();
+
+		@Override
+		public ProjectionCollector get() {
+			return instance;
+		}
+
+		@Override
+		public boolean isSingleValued() {
+			return false;
+		}
+	};
+
+	private SetProjectionCollector() {
+	}
+
+	@Override
+	public Set<V> doFinish(List<V> accumulated) {
+		return new HashSet<>( accumulated );
+	}
+}
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SimpleProjectionCollector.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SimpleProjectionCollector.java
new file mode 100644
index 00000000000..20a6a59ab2d
--- /dev/null
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SimpleProjectionCollector.java
@@ -0,0 +1,50 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.engine.search.projection.spi;
+
+import java.util.List;
+import java.util.function.Function;
+
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+
+/**
+ * A {@link ProjectionCollector} that can accumulate any number of values into a {@link List},
+ * and transforms that list into an arbitrary container using a given {@link Function}.
+ *
+ * @param <E> The type of extracted values to accumulate before being transformed.
+ * @param <V> The type of values to accumulate obtained by transforming extracted values ({@code E}).
+ * @param <R> The type of the final result containing values of type {@code V}.
+ */
+final class SimpleProjectionCollector<E, V, R> extends ListBasedProjectionCollector<E, V, R> {
+
+	static final class Provider<V, R> implements ProjectionCollector.Provider<V, R> {
+		private final Function<List<V>, R> finisher;
+
+		Provider(Function<List<V>, R> finisher) {
+			this.finisher = finisher;
+		}
+
+		@Override
+		public <T> ProjectionCollector<T, V, ?, R> get() {
+			return new SimpleProjectionCollector<>( finisher );
+		}
+
+		@Override
+		public boolean isSingleValued() {
+			return false;
+		}
+	}
+
+	private final Function<List<V>, R> finisher;
+
+	private SimpleProjectionCollector(Function<List<V>, R> finisher) {
+		this.finisher = finisher;
+	}
+
+	@Override
+	public R doFinish(List<V> accumulated) {
+		return finisher.apply( accumulated );
+	}
+}
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SingleValuedProjectionAccumulator.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SingleValuedProjectionAccumulator.java
index 4fc546e425e..ed0aad0f39c 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SingleValuedProjectionAccumulator.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SingleValuedProjectionAccumulator.java
@@ -4,22 +4,19 @@
  */
 package org.hibernate.search.engine.search.projection.spi;
 
-import java.lang.invoke.MethodHandles;
-
 import org.hibernate.search.engine.backend.types.converter.runtime.FromDocumentValueConvertContext;
 import org.hibernate.search.engine.backend.types.converter.spi.ProjectionConverter;
-import org.hibernate.search.engine.logging.impl.Log;
-import org.hibernate.search.util.common.logging.impl.LoggerFactory;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 
 /**
- * A {@link ProjectionAccumulator} that can accumulate up to one value, and will throw an exception beyond that.
+ * A {@link ProjectionCollector} that can accumulate up to one value, and will throw an exception beyond that.
  *
  * @param <E> The type of extracted values to accumulate before being transformed.
  * @param <V> The type of values to accumulate obtained by transforming extracted values ({@code E}).
  */
-final class SingleValuedProjectionAccumulator<E, V> implements ProjectionAccumulator<E, V, Object, V> {
-
-	private static final Log log = LoggerFactory.make( Log.class, MethodHandles.lookup() );
+@SuppressWarnings("deprecation")
+final class SingleValuedProjectionAccumulator<E, V> extends BaseSingleValuedProjectionCollector<E, V, V>
+		implements ProjectionAccumulator<E, V, Object, V> {
 
 	@SuppressWarnings("rawtypes")
 	static final ProjectionAccumulator.Provider PROVIDER = new ProjectionAccumulator.Provider() {
@@ -39,43 +36,6 @@ public boolean isSingleValued() {
 	private SingleValuedProjectionAccumulator() {
 	}
 
-	@Override
-	public String toString() {
-		return getClass().getSimpleName();
-	}
-
-	@Override
-	public E createInitial() {
-		return null;
-	}
-
-	@Override
-	public E accumulate(Object accumulated, E value) {
-		if ( accumulated != null ) {
-			throw log.unexpectedMultiValuedField( accumulated, value );
-		}
-		return value;
-	}
-
-	@Override
-	public int size(Object accumulated) {
-		return accumulated == null ? 0 : 1;
-	}
-
-	@Override
-	@SuppressWarnings("unchecked")
-	public E get(Object accumulated, int index) {
-		return (E) accumulated;
-	}
-
-	@Override
-	public Object transform(Object accumulated, int index, V transformed) {
-		if ( index != 0 ) {
-			throw new IndexOutOfBoundsException( "Invalid index passed to " + this + ": " + index );
-		}
-		return transformed;
-	}
-
 	@Override
 	@SuppressWarnings("unchecked")
 	public Object transformAll(Object accumulated, ProjectionConverter<? super E, ? extends V> converter,
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SortedSetComparatorProjectionCollector.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SortedSetComparatorProjectionCollector.java
new file mode 100644
index 00000000000..af8e1b2f151
--- /dev/null
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SortedSetComparatorProjectionCollector.java
@@ -0,0 +1,57 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.engine.search.projection.spi;
+
+import java.util.Comparator;
+import java.util.List;
+import java.util.SortedSet;
+import java.util.TreeSet;
+
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+
+/**
+ * A {@link ProjectionCollector} that can accumulate any number of values into a {@link SortedSet}.
+ *
+ * @param <E> The type of extracted values to accumulate before being transformed.
+ * @param <V> The type of values to accumulate obtained by transforming extracted values ({@code E}).
+ */
+final class SortedSetComparatorProjectionCollector<E, V> extends ListBasedProjectionCollector<E, V, SortedSet<V>> {
+
+	static <U, R> Provider<U, R> provider(Comparator<? super U> comparator) {
+		return new ComparatorBasedSortedSetProvider<>( comparator );
+	}
+
+	private SortedSetComparatorProjectionCollector(Comparator<? super V> comparator) {
+		this.comparator = comparator;
+	}
+
+	private final Comparator<? super V> comparator;
+
+	@Override
+	public SortedSet<V> doFinish(List<V> accumulated) {
+		TreeSet<V> set = new TreeSet<>( comparator );
+		set.addAll( accumulated );
+		return set;
+	}
+
+	@SuppressWarnings("unchecked")
+	private static class ComparatorBasedSortedSetProvider<U, R> implements Provider<U, R> {
+		private final SortedSetComparatorProjectionCollector<?, U> instance;
+
+		private ComparatorBasedSortedSetProvider(Comparator<? super U> comparator) {
+			instance = new SortedSetComparatorProjectionCollector<>( comparator );
+		}
+
+		@Override
+		public <T> ProjectionCollector<T, U, ?, R> get() {
+			return (ProjectionCollector<T, U, ?, R>) instance;
+		}
+
+		@Override
+		public boolean isSingleValued() {
+			return false;
+		}
+	}
+}
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SortedSetProjectionCollector.java b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SortedSetProjectionCollector.java
new file mode 100644
index 00000000000..418152c2e1e
--- /dev/null
+++ b/engine/src/main/java/org/hibernate/search/engine/search/projection/spi/SortedSetProjectionCollector.java
@@ -0,0 +1,44 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.engine.search.projection.spi;
+
+import java.util.List;
+import java.util.SortedSet;
+import java.util.TreeSet;
+
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+
+/**
+ * A {@link ProjectionCollector} that can accumulate any number of values into a {@link SortedSet}.
+ *
+ * @param <E> The type of extracted values to accumulate before being transformed.
+ * @param <V> The type of values to accumulate obtained by transforming extracted values ({@code E}).
+ */
+final class SortedSetProjectionCollector<E, V> extends ListBasedProjectionCollector<E, V, SortedSet<V>> {
+
+	@SuppressWarnings("rawtypes")
+	static final ProjectionCollector.Provider PROVIDER =
+			new ProjectionCollector.Provider() {
+				private final SortedSetProjectionCollector instance = new SortedSetProjectionCollector();
+
+				@Override
+				public ProjectionCollector get() {
+					return instance;
+				}
+
+				@Override
+				public boolean isSingleValued() {
+					return false;
+				}
+			};
+
+	private SortedSetProjectionCollector() {
+	}
+
+	@Override
+	public SortedSet<V> doFinish(List<V> accumulated) {
+		return new TreeSet<>( accumulated );
+	}
+}
diff --git a/engine/src/main/java/org/hibernate/search/engine/search/query/dsl/impl/DefaultSearchQuerySelectStep.java b/engine/src/main/java/org/hibernate/search/engine/search/query/dsl/impl/DefaultSearchQuerySelectStep.java
index 71d5846d564..37ec11663df 100644
--- a/engine/src/main/java/org/hibernate/search/engine/search/query/dsl/impl/DefaultSearchQuerySelectStep.java
+++ b/engine/src/main/java/org/hibernate/search/engine/search/query/dsl/impl/DefaultSearchQuerySelectStep.java
@@ -14,10 +14,10 @@
 import org.hibernate.search.engine.search.predicate.dsl.PredicateFinalStep;
 import org.hibernate.search.engine.search.predicate.dsl.SearchPredicateFactory;
 import org.hibernate.search.engine.search.predicate.dsl.SimpleBooleanPredicateClausesCollector;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.dsl.ProjectionFinalStep;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionCompositor;
 import org.hibernate.search.engine.search.query.dsl.SearchQueryOptionsStep;
 import org.hibernate.search.engine.search.query.dsl.SearchQueryWhereStep;
@@ -77,7 +77,7 @@ public <P> DefaultSearchQueryOptionsStep<P, LOS> select(SearchProjection<P> proj
 	public DefaultSearchQueryOptionsStep<List<?>, LOS> select(SearchProjection<?>... projections) {
 		return select( scope.projectionBuilders().composite()
 				.build( projections, ProjectionCompositor.fromList( projections.length ),
-						ProjectionAccumulator.single() ) );
+						ProjectionCollector.nullable() ) );
 	}
 
 	@Override
diff --git a/integrationtest/backend/elasticsearch/src/test/java/org/hibernate/search/integrationtest/backend/elasticsearch/ElasticsearchExtensionIT.java b/integrationtest/backend/elasticsearch/src/test/java/org/hibernate/search/integrationtest/backend/elasticsearch/ElasticsearchExtensionIT.java
index 026f6319ab1..14e879b645a 100644
--- a/integrationtest/backend/elasticsearch/src/test/java/org/hibernate/search/integrationtest/backend/elasticsearch/ElasticsearchExtensionIT.java
+++ b/integrationtest/backend/elasticsearch/src/test/java/org/hibernate/search/integrationtest/backend/elasticsearch/ElasticsearchExtensionIT.java
@@ -47,6 +47,7 @@
 import org.hibernate.search.engine.search.common.ValueModel;
 import org.hibernate.search.engine.search.loading.spi.SearchLoadingContext;
 import org.hibernate.search.engine.search.predicate.SearchPredicate;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.query.SearchQuery;
 import org.hibernate.search.engine.search.sort.SearchSort;
@@ -1107,7 +1108,7 @@ void jsonHitProjectionInsideNested() {
 		assertThatThrownBy( () -> mainIndex.createScope().query()
 				.select( f -> f.object( "nestedObject" ).from(
 						f.extension( ElasticsearchExtension.get() ).jsonHit()
-				).asList().multi()
+				).asList().collector( ProjectionCollector.list() )
 				)
 				.where( f -> f.matchAll() )
 				.toQuery()
@@ -1123,7 +1124,7 @@ void sourceProjectionInsideNested() {
 		assertThatThrownBy( () -> mainIndex.createScope().query()
 				.select( f -> f.object( "nestedObject" ).from(
 						f.extension( ElasticsearchExtension.get() ).source()
-				).asList().multi()
+				).asList().collector( ProjectionCollector.list() )
 				)
 				.where( f -> f.matchAll() )
 				.toQuery()
@@ -1139,7 +1140,7 @@ void explanationProjectionInsideNested() {
 		assertThatThrownBy( () -> mainIndex.createScope().query()
 				.select( f -> f.object( "nestedObject" ).from(
 						f.extension( ElasticsearchExtension.get() ).explanation()
-				).asList().multi()
+				).asList().collector( ProjectionCollector.list() )
 				)
 				.where( f -> f.matchAll() )
 				.toQuery()
diff --git a/integrationtest/backend/elasticsearch/src/test/java/org/hibernate/search/integrationtest/backend/elasticsearch/testsupport/util/ElasticsearchTckBackendFeatures.java b/integrationtest/backend/elasticsearch/src/test/java/org/hibernate/search/integrationtest/backend/elasticsearch/testsupport/util/ElasticsearchTckBackendFeatures.java
index bf92608302b..70aaa2fb4e3 100644
--- a/integrationtest/backend/elasticsearch/src/test/java/org/hibernate/search/integrationtest/backend/elasticsearch/testsupport/util/ElasticsearchTckBackendFeatures.java
+++ b/integrationtest/backend/elasticsearch/src/test/java/org/hibernate/search/integrationtest/backend/elasticsearch/testsupport/util/ElasticsearchTckBackendFeatures.java
@@ -22,6 +22,7 @@
 import java.time.ZoneOffset;
 import java.time.ZonedDateTime;
 import java.time.temporal.TemporalAccessor;
+import java.util.ArrayList;
 import java.util.Comparator;
 import java.util.LinkedHashMap;
 import java.util.Locale;
@@ -31,6 +32,7 @@
 import org.hibernate.search.backend.elasticsearch.types.format.impl.ElasticsearchDefaultFieldFormatProvider;
 import org.hibernate.search.engine.backend.types.VectorSimilarity;
 import org.hibernate.search.engine.cfg.spi.FormatUtils;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.spatial.GeoPoint;
 import org.hibernate.search.integrationtest.backend.tck.testsupport.types.BigDecimalFieldTypeDescriptor;
 import org.hibernate.search.integrationtest.backend.tck.testsupport.types.FieldTypeDescriptor;
@@ -514,4 +516,15 @@ public <F> boolean rawAggregationProduceSensibleDoubleValue(FieldTypeDescriptor<
 		}
 		return super.rawAggregationProduceSensibleDoubleValue( fFieldTypeDescriptor );
 	}
+
+	@Override
+	public <U, R> R accumulatedNullValue(ProjectionCollector.Provider<U, R> collector) {
+		return accumulatedNullValue( collector.get() );
+	}
+
+	private <U, R, A> R accumulatedNullValue(ProjectionCollector<Object, U, A, R> collector) {
+		ArrayList<Object> values = new ArrayList<>();
+		values.add( null );
+		return collector.finish( collector.accumulateAll( collector.createInitial(), values ) );
+	}
 }
diff --git a/integrationtest/backend/lucene/src/test/java/org/hibernate/search/integrationtest/backend/lucene/LuceneExtensionIT.java b/integrationtest/backend/lucene/src/test/java/org/hibernate/search/integrationtest/backend/lucene/LuceneExtensionIT.java
index c0c5d764b18..006f1b671bc 100644
--- a/integrationtest/backend/lucene/src/test/java/org/hibernate/search/integrationtest/backend/lucene/LuceneExtensionIT.java
+++ b/integrationtest/backend/lucene/src/test/java/org/hibernate/search/integrationtest/backend/lucene/LuceneExtensionIT.java
@@ -54,6 +54,7 @@
 import org.hibernate.search.engine.search.common.ValueModel;
 import org.hibernate.search.engine.search.loading.spi.SearchLoadingContext;
 import org.hibernate.search.engine.search.predicate.SearchPredicate;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.query.SearchQuery;
 import org.hibernate.search.engine.search.sort.SearchSort;
@@ -887,7 +888,7 @@ void documentProjectionInsideNested() {
 		assertThatThrownBy( () -> mainIndex.createScope().query()
 				.select( f -> f.object( "nestedObject" ).from(
 						f.extension( LuceneExtension.get() ).document()
-				).asList().multi()
+				).asList().collector( ProjectionCollector.list() )
 				)
 				.where( f -> f.matchAll() )
 				.toQuery()
@@ -903,7 +904,7 @@ void explanationProjectionInsideNested() {
 		assertThatThrownBy( () -> mainIndex.createScope().query()
 				.select( f -> f.object( "nestedObject" ).from(
 						f.extension( LuceneExtension.get() ).explanation()
-				).asList().multi()
+				).asList().collector( ProjectionCollector.list() )
 				)
 				.where( f -> f.matchAll() )
 				.toQuery()
@@ -933,8 +934,9 @@ void documentTreeMultipleIndexes() {
 				someOtherIndex.query().select( f -> f.object( "someOtherNestedObject" ).from( f
 						.object( "someOtherNestedObject.someOtherNestedNestedObject" )
 						.from( f.field( "someOtherNestedObject.someOtherNestedNestedObject.nestedNestedSomeOtherInteger" )
-								.multi() )
-						.asList().multi() ).asList().multi() )
+								.collector( ProjectionCollector.list() ) )
+						.asList().collector( ProjectionCollector.list() ) ).asList()
+						.collector( ProjectionCollector.list() ) )
 						.where( f -> f.match().field( "someOtherString" ).matching( "text 2" ) ).fetchAllHits()
 		).containsExactly(
 				List.of(
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/highlight/AbstractHighlighterIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/highlight/AbstractHighlighterIT.java
index 6cbd5f4aea4..34e1afbb67a 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/highlight/AbstractHighlighterIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/highlight/AbstractHighlighterIT.java
@@ -14,7 +14,11 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.Optional;
 import java.util.Set;
+import java.util.SortedSet;
+import java.util.TreeSet;
+import java.util.stream.Collectors;
 
 import org.hibernate.search.engine.backend.document.IndexFieldReference;
 import org.hibernate.search.engine.backend.document.IndexObjectFieldReference;
@@ -137,6 +141,58 @@ void highlighterNoConfigurationAtAll() {
 				);
 	}
 
+	@Test
+	void collectAsSet() {
+		StubMappingScope scope = index.createScope();
+
+		SearchQuery<Set<String>> highlights = scope.query().select(
+				f -> f.highlight( "string" ).set()
+		)
+				.where( f -> f.match().field( "string" ).matching( "another" ) )
+				.toQuery();
+
+		assertThatHits( highlights.fetchAllHits() )
+				.hasHitsAnyOrder(
+						Set.of( "some <em>another</em> value" ),
+						Set.of( "some yet <em>another</em> value" )
+				);
+	}
+
+	@Test
+	void collectAsSortedSet() {
+		StubMappingScope scope = index.createScope();
+
+		SearchQuery<SortedSet<String>> highlights = scope.query().select(
+				f -> f.highlight( "string" ).sortedSet()
+		)
+				.where( f -> f.match().field( "string" ).matching( "another" ) )
+				.toQuery();
+
+		assertThatHits( highlights.fetchAllHits() )
+				.hasHitsAnyOrder(
+						new TreeSet<>( Set.of( "some <em>another</em> value" ) ),
+						new TreeSet<>( Set.of( "some yet <em>another</em> value" )
+						)
+				);
+	}
+
+	@Test
+	void collectAsArray() {
+		StubMappingScope scope = index.createScope();
+
+		SearchQuery<String[]> highlights = scope.query().select(
+				f -> f.highlight( "string" ).array()
+		)
+				.where( f -> f.match().field( "string" ).matching( "another" ) )
+				.toQuery();
+
+		assertThatHits( highlights.fetchAllHits() )
+				.hasHitsAnyOrder(
+						new String[] { "some <em>another</em> value" },
+						new String[] { "some yet <em>another</em> value" }
+				);
+	}
+
 	@Test
 	void highlighterNoSettings() {
 		StubMappingScope scope = index.createScope();
@@ -443,7 +499,25 @@ void numberOfFragmentsSingle() {
 		StubMappingScope scope = index.createScope();
 
 		SearchQuery<String> highlights = scope.query().select(
-				f -> f.highlight( "anotherString" ).single()
+				f -> f.highlight( "anotherString" ).nullable()
+		)
+				.where( f -> f.match().field( "anotherString" ).matching( "ipsum" ) )
+				.highlighter( h -> highlighter( h ).numberOfFragments( 1 ) )
+				.toQuery();
+
+		assertThatHits( highlights.fetchAllHits() )
+				.hasHitsAnyOrder(
+						numberOfFragmentsResult()
+				);
+	}
+
+
+	@Test
+	void numberOfFragmentsSingleOptional() {
+		StubMappingScope scope = index.createScope();
+
+		SearchQuery<Optional<String>> highlights = scope.query().select(
+				f -> f.highlight( "anotherString" ).optional()
 		)
 				.where( f -> f.match().field( "anotherString" ).matching( "ipsum" ) )
 				.highlighter( h -> highlighter( h ).numberOfFragments( 1 ) )
@@ -452,10 +526,13 @@ void numberOfFragmentsSingle() {
 		assertThatHits( highlights.fetchAllHits() )
 				.hasHitsAnyOrder(
 						numberOfFragmentsResult()
+								.stream().map( Optional::of )
+								.collect( Collectors.toList() )
 				);
 	}
 
 	@Test
+	@Deprecated(since = "8.0")
 	void numberOfFragmentsSingleNamedHighlighter() {
 		StubMappingScope scope = index.createScope();
 
@@ -472,8 +549,9 @@ void numberOfFragmentsSingleNamedHighlighter() {
 				);
 	}
 
+	@Deprecated
 	@Test
-	void numberOfFragmentsSingleError() {
+	void numberOfFragmentsSingleErrorSingle() {
 		StubMappingScope scope = index.createScope();
 
 		// numberOfFragments > 1
@@ -499,8 +577,9 @@ void numberOfFragmentsSingleError() {
 						"A single-valued highlight projection requested, but the corresponding highlighter does not set number of fragments to 1" );
 	}
 
+	@Deprecated
 	@Test
-	void numberOfFragmentsSingleButNoExpectedValuesReturned() {
+	void numberOfFragmentsSingleButNoExpectedValuesReturnedSingle() {
 		StubMappingScope scope = index.createScope();
 
 		SearchQuery<String> highlights = scope.query().select(
@@ -514,6 +593,48 @@ void numberOfFragmentsSingleButNoExpectedValuesReturned() {
 				.hasHitsAnyOrder( List.of() );
 	}
 
+	@Test
+	void numberOfFragmentsSingleError() {
+		StubMappingScope scope = index.createScope();
+
+		// numberOfFragments > 1
+		assertThatThrownBy( () -> scope.query().select(
+				f -> f.highlight( "anotherString" ).nullable()
+		)
+				.where( f -> f.match().field( "anotherString" ).matching( "ipsum" ) )
+				.highlighter( h -> highlighter( h ).numberOfFragments( 2 ) )
+				.toQuery()
+		).isInstanceOf( SearchException.class )
+				.hasMessageContainingAll(
+						"A single-valued highlight projection requested, but the corresponding highlighter does not set number of fragments to 1" );
+
+		// numberOfFragments not defined
+		assertThatThrownBy( () -> scope.query().select(
+				f -> f.highlight( "anotherString" ).nullable()
+		)
+				.where( f -> f.match().field( "anotherString" ).matching( "ipsum" ) )
+				.highlighter( h -> highlighter( h ) )
+				.toQuery()
+		).isInstanceOf( SearchException.class )
+				.hasMessageContainingAll(
+						"A single-valued highlight projection requested, but the corresponding highlighter does not set number of fragments to 1" );
+	}
+
+	@Test
+	void numberOfFragmentsSingleButNoExpectedValuesReturned() {
+		StubMappingScope scope = index.createScope();
+
+		SearchQuery<String> highlights = scope.query().select(
+				f -> f.highlight( "anotherString" ).nullable()
+		)
+				.where( f -> f.match().field( "anotherString" ).matching( "thisCannotBeMatchedToAnythingInTheText" ) )
+				.highlighter( h -> highlighter( h ).numberOfFragments( 1 ) )
+				.toQuery();
+
+		assertThatHits( highlights.fetchAllHits() )
+				.hasHitsAnyOrder( List.of() );
+	}
+
 	protected List<String> numberOfFragmentsResult() {
 		return Arrays.asList(
 				"Lorem <em>ipsum</em> dolor sit amet, consectetur adipiscing elit."
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/predicate/KnnPredicateSpecificsIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/predicate/KnnPredicateSpecificsIT.java
index 2fb6ab03690..99dc34d185d 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/predicate/KnnPredicateSpecificsIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/predicate/KnnPredicateSpecificsIT.java
@@ -36,6 +36,7 @@
 import org.hibernate.search.engine.backend.types.dsl.SearchableProjectableIndexFieldTypeOptionsStep;
 import org.hibernate.search.engine.search.predicate.dsl.KnnPredicateOptionsStep;
 import org.hibernate.search.engine.search.predicate.dsl.SearchPredicateFactory;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
 import org.hibernate.search.engine.search.query.SearchQuery;
 import org.hibernate.search.integrationtest.backend.tck.testsupport.types.FieldTypeDescriptor;
@@ -775,7 +776,7 @@ void nestedVector() {
 															f.field( "nested.floatVector" )
 													)
 													.asList()
-													.multi()
+													.collector( ProjectionCollector.list() )
 									).asList()
 							).where(
 									f -> f.knn( 1 ).field( "nested.byteVector" ).matching( bytes( 2, (byte) -120 ) )
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/AbstractCompositeProjectionFromAsIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/AbstractCompositeProjectionFromAsIT.java
index ee8cad1044a..36938735b6b 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/AbstractCompositeProjectionFromAsIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/AbstractCompositeProjectionFromAsIT.java
@@ -5,12 +5,17 @@
 package org.hibernate.search.integrationtest.backend.tck.search.projection;
 
 import static org.hibernate.search.util.impl.integrationtest.common.assertion.SearchResultAssert.assertThatQuery;
+import static org.junit.jupiter.api.Assumptions.assumeTrue;
 import static org.mockito.Mockito.when;
 
 import java.time.LocalDate;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
+import java.util.SortedSet;
+import java.util.TreeSet;
 import java.util.function.BiFunction;
 import java.util.function.Function;
 import java.util.function.IntFunction;
@@ -20,6 +25,7 @@
 import org.hibernate.search.engine.backend.document.DocumentElement;
 import org.hibernate.search.engine.backend.document.model.dsl.IndexSchemaElement;
 import org.hibernate.search.engine.backend.types.Projectable;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.definition.spi.ProjectionRegistry;
 import org.hibernate.search.engine.search.projection.dsl.CompositeProjectionFrom1AsStep;
 import org.hibernate.search.engine.search.projection.dsl.CompositeProjectionFrom2AsStep;
@@ -109,7 +115,8 @@ public void asList_transformer_flexibleFunctionArgumentTypes() {
 		@Test
 		public void asList_multi() {
 			assertThatQuery( index.query()
-					.select( f -> doFromForMulti( f, startProjectionForMulti( f ) ).asList().multi() )
+					.select( f -> doFromForMulti( f, startProjectionForMulti( f ) ).asList()
+							.collector( ProjectionCollector.list() ) )
 					.where( f -> f.matchAll() ) )
 					.hasHitsAnyOrder( expectedListsForMulti() );
 		}
@@ -151,12 +158,25 @@ public void asArray_transformer_flexibleFunctionArgumentTypes() {
 		@Test
 		public void asArray_multi() {
 			assertThatQuery( index.query()
-					.select( f -> doFromForMulti( f, startProjectionForMulti( f ) ).asArray().multi() )
+					.select( f -> doFromForMulti( f, startProjectionForMulti( f ) ).asArray()
+							.collector( ProjectionCollector.list() ) )
 					.where( f -> f.matchAll() ) )
 					.hits().asIs().usingRecursiveFieldByFieldElementComparator()
 					.containsExactlyInAnyOrderElementsOf( expectedArraysForMulti() );
 		}
 
+		@Test
+		public void asArray_set() {
+			assertThatQuery( index.query()
+					.select( f -> doFromForMulti( f, startProjectionForMulti( f ) ).asArray()
+							.collector( ProjectionCollector.set() ) )
+					.where( f -> f.matchAll() ) )
+					.hits().asIs().usingRecursiveFieldByFieldElementComparator()
+					.containsExactlyInAnyOrderElementsOf( expectedArraysForMulti()
+							.stream().map( HashSet::new )
+							.toList() );
+		}
+
 		@Test
 		@TestForIssue(jiraKey = "HSEARCH-3927")
 		public void as_class() {
@@ -195,7 +215,8 @@ public void as_class_multi() {
 				doFrom( f, index.binding().compositeForMulti(), CompositeBinding::relativePath, initialStep )
 						.asArray( ValueWrapper<Object[]>::new ) );
 				assertThatQuery( index.createScope().query()
-						.select( f -> startProjectionForMulti( f ).as( ValueWrapper.class ).multi() )
+						.select( f -> startProjectionForMulti( f ).as( ValueWrapper.class )
+								.collector( ProjectionCollector.list() ) )
 						.where( f -> f.matchAll() ) )
 						.hits().asIs().usingRecursiveFieldByFieldElementComparator()
 						.containsExactlyInAnyOrderElementsOf( expectedArraysForMulti().stream()
@@ -269,6 +290,15 @@ public void as_transformer() {
 					.hasHitsAnyOrder( expectedTransformed() );
 		}
 
+		@Test
+		public void as_transformer_accumulator() {
+			assertThatQuery( index.query()
+					.select( f -> doAs( doFromForMulti( f, startProjectionForMulti( f ) ) ).list() )
+					.where( f -> f.matchAll() ) )
+					.hasHitsAnyOrder( expectedTransformedForMulti() );
+		}
+
+		@Deprecated
 		@Test
 		public void as_transformer_multi() {
 			assertThatQuery( index.query()
@@ -277,6 +307,35 @@ public void as_transformer_multi() {
 					.hasHitsAnyOrder( expectedTransformedForMulti() );
 		}
 
+		@Test
+		public void as_transformer_set() {
+			assertThatQuery( index.query()
+					.select( f -> doAs( doFromForMulti( f, startProjectionForMulti( f ) ) ).set() )
+					.where( f -> f.matchAll() ) )
+					.hasHitsAnyOrder( expectedTransformedForMulti()
+							.stream()
+							.map( l -> (Set<T>) new HashSet<>( l ) )
+							.toList()
+					);
+		}
+
+		@Test
+		public void as_transformer_sortedSet() {
+			Collection<List<T>> lists = expectedTransformedForMulti();
+			assumeTrue(
+					lists.iterator().next().get( 0 ) instanceof Comparable,
+					"This test only makes sense for comparable types"
+			);
+
+			assertThatQuery( index.query()
+					.select( f -> doAs( doFromForMulti( f, startProjectionForMulti( f ) ) ).sortedSet() )
+					.where( f -> f.matchAll() ) )
+					.hasHitsAnyOrder( lists.stream()
+							.map( l -> (SortedSet<T>) new TreeSet<>( l ) )
+							.toList()
+					);
+		}
+
 		@Override
 		protected final S doFrom(SearchProjectionFactory<?, ?> f, CompositeProjectionInnerStep step) {
 			return doFrom( f, index.binding().composite(), CompositeBinding::absolutePath, step );
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/AbstractDistanceProjectionSingleValuedBaseIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/AbstractDistanceProjectionSingleValuedBaseIT.java
index fd08b53941c..0ae726e901e 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/AbstractDistanceProjectionSingleValuedBaseIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/AbstractDistanceProjectionSingleValuedBaseIT.java
@@ -84,7 +84,7 @@ public static List<? extends Arguments> params() {
 	@RegisterExtension
 	public static SearchSetupHelper setupHelper = SearchSetupHelper.create();
 
-	private static final SimpleMappedIndex<SingleFieldIndexBinding> mainIndex =
+	protected static final SimpleMappedIndex<SingleFieldIndexBinding> mainIndex =
 			SimpleMappedIndex.of(
 					root -> SingleFieldIndexBinding.createWithSingleValuedNestedFields(
 							root,
@@ -435,7 +435,7 @@ void factoryWithRoot(TestedFieldStructure fieldStructure, DataSet dataSet) {
 				);
 	}
 
-	private String getFieldPath(TestedFieldStructure fieldStructure) {
+	protected String getFieldPath(TestedFieldStructure fieldStructure) {
 		return mainIndex.binding().getFieldPath( fieldStructure, fieldType );
 	}
 
@@ -456,9 +456,9 @@ protected abstract ProjectionFinalStep<Double> distance(
 	protected abstract SortFinalStep sort(SearchSortFactory sort, String path, GeoPoint center,
 			String parameterName);
 
-	private static class DataSet {
-		private final TestedFieldStructure fieldStructure;
-		private final String routingKey;
+	protected static class DataSet {
+		protected final TestedFieldStructure fieldStructure;
+		protected final String routingKey;
 
 		private DataSet(TestedFieldStructure fieldStructure) {
 			this.fieldStructure = fieldStructure;
@@ -506,7 +506,7 @@ private GeoPoint getSortableFieldValue(int documentNumber) {
 			return AscendingUniqueDistanceFromCenterValues.INSTANCE.getSingle().get( documentNumber - 1 );
 		}
 
-		private double getFieldDistanceFromCenter1(int documentNumber) {
+		protected double getFieldDistanceFromCenter1(int documentNumber) {
 			return IndexableGeoPointWithDistanceFromCenterValues.INSTANCE.getSingleDistancesFromCenterPoint1()
 					.get( documentNumber - 1 );
 		}
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/AbstractProjectionInObjectProjectionIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/AbstractProjectionInObjectProjectionIT.java
index 985357c9a42..869554a75e3 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/AbstractProjectionInObjectProjectionIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/AbstractProjectionInObjectProjectionIT.java
@@ -21,6 +21,7 @@
 import org.hibernate.search.engine.backend.types.ObjectStructure;
 import org.hibernate.search.engine.backend.types.Projectable;
 import org.hibernate.search.engine.backend.types.dsl.SearchableProjectableIndexFieldTypeOptionsStep;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.dsl.ProjectionFinalStep;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
 import org.hibernate.search.integrationtest.backend.tck.testsupport.types.FieldTypeDescriptor;
@@ -90,10 +91,10 @@ void objectOnLevel1AndObjectOnLevel2(SimpleMappedIndex<IndexBinding> mainIndex,
 																		mainIndex, dataSet ), dataSet )
 														)
 														.as( ObjectDto::new )
-														.multi()
+														.collector( ProjectionCollector.list() )
 										)
 										.as( Level1ObjectDto::new )
-										.multi()
+										.collector( ProjectionCollector.list() )
 						)
 						.as( IdAndObjectDto::new ) )
 				.where( f -> f.matchAll() )
@@ -256,7 +257,7 @@ void objectOnLevel1AndNoLevel2(SimpleMappedIndex<IndexBinding> mainIndex,
 												), dataSet )
 										)
 										.as( ObjectDto::new )
-										.multi()
+										.collector( ProjectionCollector.list() )
 						)
 						.as( IdAndObjectDto::new ) )
 				.where( f -> f.matchAll() )
@@ -362,7 +363,7 @@ void objectOnLevel1AndFlattenedLevel2(SimpleMappedIndex<IndexBinding> mainIndex,
 														.as( FlattenedObjectDto::new )
 										)
 										.as( Level1ObjectWithFlattenedLevel2Dto::new )
-										.multi()
+										.collector( ProjectionCollector.list() )
 						)
 						.as( IdAndObjectDto::new ) )
 				.where( f -> f.matchAll() )
@@ -562,7 +563,7 @@ void noLevel1AndObjectOnLevel2(SimpleMappedIndex<IndexBinding> mainIndex,
 												), dataSet )
 										)
 										.as( ObjectDto::new )
-										.multi()
+										.collector( ProjectionCollector.list() )
 						)
 						.as( IdAndObjectDto::new ) )
 				.where( f -> f.matchAll() )
@@ -663,7 +664,7 @@ void flattenedLevel1AndObjectOnLevel2(SimpleMappedIndex<IndexBinding> mainIndex,
 																		mainIndex, dataSet ), dataSet )
 														)
 														.as( ObjectDto::new )
-														.multi()
+														.collector( ProjectionCollector.list() )
 										)
 										.as( FlattenedLevel1ObjectDto::new )
 						)
@@ -789,7 +790,7 @@ void fieldOutsideObjectFieldTree(SimpleMappedIndex<IndexBinding> mainIndex,
 								)
 						)
 						.asList()
-						.multi() )
+						.collector( ProjectionCollector.list() ) )
 				.where( f -> f.matchAll() )
 				.routing( dataSet.routingKey )
 				.toQuery() )
@@ -836,7 +837,7 @@ void singleValuedField_effectivelyMultiValuedInContext(SimpleMappedIndex<IndexBi
 										.asList()
 						)
 						.asList()
-						.multi() )
+						.collector( ProjectionCollector.list() ) )
 				.where( f -> f.matchAll() )
 				.routing( dataSet.routingKey )
 				.toQuery() )
@@ -847,13 +848,13 @@ void singleValuedField_effectivelyMultiValuedInContext(SimpleMappedIndex<IndexBi
 						) + "'",
 						"the projection is single-valued, but this field is effectively multi-valued in this context",
 						"because parent object field '" + level2Path( mainIndex, dataSet ) + "' is multi-valued",
-						"call '.multi()' when you create the projection on field '" + level2SingleValuedFieldPath(
+						"call '.collector(...)' when you create the projection on field '" + level2SingleValuedFieldPath(
 								mainIndex, dataSet ) + "'",
 						"or wrap that projection in an object projection like this:"
 								+ " 'f.object(\"" + level2Path( mainIndex, dataSet ) + "\").from(<the projection on field "
 								+ level2SingleValuedFieldPath(
 										mainIndex, dataSet )
-								+ ">).as(...).multi()'."
+								+ ">).as(...).collector(...)'."
 				);
 	}
 
@@ -891,10 +892,10 @@ void missingFields(SimpleMappedIndex<IndexBinding> mainIndex,
 																		mainIndex, dataSet ), dataSet )
 														)
 														.as( ObjectDto::new )
-														.multi()
+														.collector( ProjectionCollector.list() )
 										)
 										.as( Level1ObjectDto::new )
-										.multi()
+										.collector( ProjectionCollector.list() )
 						)
 						.as( IdAndObjectDto::new ) )
 				.where( f -> f.matchAll() )
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionBaseIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionBaseIT.java
index 931693eee14..cddafd71461 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionBaseIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionBaseIT.java
@@ -9,6 +9,7 @@
 
 import org.hibernate.search.engine.backend.types.ObjectStructure;
 import org.hibernate.search.engine.backend.types.dsl.SearchableProjectableIndexFieldTypeOptionsStep;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.dsl.ProjectionFinalStep;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
 import org.hibernate.search.engine.spatial.GeoPoint;
@@ -153,7 +154,8 @@ protected ProjectionFinalStep<Double> singleValuedProjection(SearchProjectionFac
 		@Override
 		protected ProjectionFinalStep<List<Double>> multiValuedProjection(SearchProjectionFactory<?, ?> f,
 				String absoluteFieldPath, DataSet<GeoPoint, Double, DistanceProjectionTestValues> dataSet) {
-			return f.distance( absoluteFieldPath, dataSet.values.projectionCenterPoint() ).multi();
+			return f.distance( absoluteFieldPath, dataSet.values.projectionCenterPoint() )
+					.collector( ProjectionCollector.list() );
 		}
 
 	}
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionMultiValuedAccumulatorBaseIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionMultiValuedAccumulatorBaseIT.java
new file mode 100644
index 00000000000..b1f05619d73
--- /dev/null
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionMultiValuedAccumulatorBaseIT.java
@@ -0,0 +1,46 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.search.integrationtest.backend.tck.search.projection;
+
+import java.util.List;
+
+import org.hibernate.search.engine.backend.common.DocumentReference;
+import org.hibernate.search.engine.common.EntityReference;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+import org.hibernate.search.engine.search.projection.dsl.ProjectionFinalStep;
+import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
+import org.hibernate.search.engine.search.query.dsl.SearchQueryOptionsStep;
+import org.hibernate.search.engine.search.sort.dsl.SearchSortFactory;
+import org.hibernate.search.engine.search.sort.dsl.SortFinalStep;
+import org.hibernate.search.engine.spatial.DistanceUnit;
+import org.hibernate.search.engine.spatial.GeoPoint;
+
+class DistanceProjectionMultiValuedAccumulatorBaseIT extends AbstractDistanceProjectionMultiValuedBaseIT {
+
+	@Override
+	protected void addParameter(SearchQueryOptionsStep<?, ?, ?, ?, ?> query, String parameterName, Object value) {
+		// do nothing
+	}
+
+	@Override
+	protected ProjectionFinalStep<List<Double>> distance(
+			SearchProjectionFactory<EntityReference, DocumentReference> projection, String path, GeoPoint center,
+			String parameterName) {
+		return projection.distance( path, center ).collector( ProjectionCollector.list() );
+	}
+
+	@Override
+	protected ProjectionFinalStep<List<Double>> distance(
+			SearchProjectionFactory<EntityReference, DocumentReference> projection, String path, GeoPoint center,
+			DistanceUnit unit, String centerParam, String unitParam) {
+		return projection.distance( path, center ).collector( ProjectionCollector.list() ).unit( unit );
+	}
+
+	@Override
+	protected SortFinalStep sort(SearchSortFactory sort, String path, GeoPoint center,
+			String parameterName) {
+		return sort.distance( path, center );
+	}
+}
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionMultiValuedBaseIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionMultiValuedBaseIT.java
index bf9e888dc4d..ccd492c66de 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionMultiValuedBaseIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionMultiValuedBaseIT.java
@@ -16,6 +16,7 @@
 import org.hibernate.search.engine.spatial.DistanceUnit;
 import org.hibernate.search.engine.spatial.GeoPoint;
 
+@Deprecated(since = "8.0")
 class DistanceProjectionMultiValuedBaseIT extends AbstractDistanceProjectionMultiValuedBaseIT {
 
 	@Override
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionParameterMultiValuedBaseIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionParameterMultiValuedBaseIT.java
index 8a7fabc7371..a91578301d2 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionParameterMultiValuedBaseIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionParameterMultiValuedBaseIT.java
@@ -8,6 +8,7 @@
 
 import org.hibernate.search.engine.backend.common.DocumentReference;
 import org.hibernate.search.engine.common.EntityReference;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.dsl.ProjectionFinalStep;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
 import org.hibernate.search.engine.search.query.dsl.SearchQueryOptionsStep;
@@ -30,7 +31,8 @@ protected ProjectionFinalStep<List<Double>> distance(
 			SearchProjectionFactory<EntityReference, DocumentReference> projection, String path, GeoPoint center,
 			String parameterName) {
 		return projection.withParameters(
-				params -> projection.distance( path, params.get( parameterName, GeoPoint.class ) ).multi() );
+				params -> projection.distance( path, params.get( parameterName, GeoPoint.class ) )
+						.collector( ProjectionCollector.list() ) );
 	}
 
 	@Override
@@ -38,7 +40,8 @@ protected ProjectionFinalStep<List<Double>> distance(
 			SearchProjectionFactory<EntityReference, DocumentReference> projection, String path, GeoPoint center,
 			DistanceUnit unit, String centerParam, String unitParam) {
 		return projection.withParameters(
-				params -> projection.distance( path, params.get( centerParam, GeoPoint.class ) ).multi()
+				params -> projection.distance( path, params.get( centerParam, GeoPoint.class ) )
+						.collector( ProjectionCollector.list() )
 						.unit( params.get( unitParam, DistanceUnit.class ) ) );
 	}
 
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionParameterSingleValuedBaseIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionParameterSingleValuedBaseIT.java
index fe07f7b79e2..ed0be013f2d 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionParameterSingleValuedBaseIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionParameterSingleValuedBaseIT.java
@@ -8,6 +8,7 @@
 
 import org.hibernate.search.engine.backend.common.DocumentReference;
 import org.hibernate.search.engine.common.EntityReference;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.dsl.ProjectionFinalStep;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
 import org.hibernate.search.engine.search.query.dsl.SearchQueryOptionsStep;
@@ -37,7 +38,8 @@ protected ProjectionFinalStep<List<Double>> distanceMulti(
 			SearchProjectionFactory<EntityReference, DocumentReference> projection, String path, GeoPoint center,
 			String parameterName) {
 		return projection.withParameters(
-				params -> projection.distance( path, params.get( parameterName, GeoPoint.class ) ).multi() );
+				params -> projection.distance( path, params.get( parameterName, GeoPoint.class ) )
+						.collector( ProjectionCollector.list() ) );
 	}
 
 	@Override
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionSingleValuedBaseIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionSingleValuedBaseIT.java
index 0c1d4dffed7..c879f65a3fd 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionSingleValuedBaseIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionSingleValuedBaseIT.java
@@ -4,10 +4,19 @@
  */
 package org.hibernate.search.integrationtest.backend.tck.search.projection;
 
+import static org.hibernate.search.integrationtest.backend.tck.testsupport.types.values.IndexableGeoPointWithDistanceFromCenterValues.CENTER_POINT_1;
+import static org.hibernate.search.util.impl.integrationtest.common.assertion.SearchResultAssert.assertThatQuery;
+import static org.hibernate.search.util.impl.integrationtest.common.assertion.TestComparators.APPROX_M_COMPARATOR;
+
+import java.util.Comparator;
 import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
 
 import org.hibernate.search.engine.backend.common.DocumentReference;
 import org.hibernate.search.engine.common.EntityReference;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.dsl.DistanceToFieldProjectionOptionsStep;
 import org.hibernate.search.engine.search.projection.dsl.DistanceToFieldProjectionValueStep;
 import org.hibernate.search.engine.search.projection.dsl.ProjectionFinalStep;
@@ -17,9 +26,123 @@
 import org.hibernate.search.engine.search.sort.dsl.SortFinalStep;
 import org.hibernate.search.engine.spatial.DistanceUnit;
 import org.hibernate.search.engine.spatial.GeoPoint;
+import org.hibernate.search.integrationtest.backend.tck.testsupport.util.TckConfiguration;
+import org.hibernate.search.integrationtest.backend.tck.testsupport.util.TestedFieldStructure;
+import org.hibernate.search.util.impl.integrationtest.common.assertion.TestComparators;
+import org.hibernate.search.util.impl.integrationtest.mapper.stub.StubMappingScope;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
 
 class DistanceProjectionSingleValuedBaseIT extends AbstractDistanceProjectionSingleValuedBaseIT {
 
+	@ParameterizedTest(name = "{0}")
+	@MethodSource("params")
+	void optional(TestedFieldStructure fieldStructure, DataSet dataSet) {
+		StubMappingScope scope = mainIndex.createScope();
+
+		String fieldPath = getFieldPath( fieldStructure );
+
+		var projection = scope.projection().distance( fieldPath, CENTER_POINT_1 ).optional().toProjection();
+
+		var query = scope.query()
+				// Do NOT add any additional projection here: this serves as a non-regression test for HSEARCH-3618
+				.select( projection )
+				.where( f -> f.matchAll() );
+		addParameter( query, "center-param", CENTER_POINT_1 );
+
+		assertThatQuery( query.routing( dataSet.routingKey ).toQuery() )
+				.hits().asIs()
+				.usingElementComparator( TestComparators.optional( APPROX_M_COMPARATOR ) )
+				.containsExactlyInAnyOrder(
+						Optional.of( dataSet.getFieldDistanceFromCenter1( 1 ) ),
+						Optional.of( dataSet.getFieldDistanceFromCenter1( 2 ) ),
+						Optional.of( dataSet.getFieldDistanceFromCenter1( 3 ) ),
+						Optional.empty() // Empty document
+				);
+	}
+
+	@ParameterizedTest(name = "{0}")
+	@MethodSource("params")
+	void set(TestedFieldStructure fieldStructure, DataSet dataSet) {
+		StubMappingScope scope = mainIndex.createScope();
+
+		String fieldPath = getFieldPath( fieldStructure );
+
+		var projection = scope.projection().distance( fieldPath, CENTER_POINT_1 ).set().toProjection();
+
+		var query = scope.query()
+				// Do NOT add any additional projection here: this serves as a non-regression test for HSEARCH-3618
+				.select( projection )
+				.where( f -> f.matchAll() );
+		addParameter( query, "center-param", CENTER_POINT_1 );
+
+		assertThatQuery( query.routing( dataSet.routingKey ).toQuery() )
+				.hits().asIs()
+				.usingElementComparator( TestComparators.lexicographic( APPROX_M_COMPARATOR ) )
+				.containsExactlyInAnyOrder(
+						Set.of( dataSet.getFieldDistanceFromCenter1( 1 ) ),
+						Set.of( dataSet.getFieldDistanceFromCenter1( 2 ) ),
+						Set.of( dataSet.getFieldDistanceFromCenter1( 3 ) ),
+						TckConfiguration.get().getBackendFeatures().accumulatedNullValue( ProjectionCollector.set() ) // Empty document
+				);
+	}
+
+	@ParameterizedTest(name = "{0}")
+	@MethodSource("params")
+	void sortedSet(TestedFieldStructure fieldStructure, DataSet dataSet) {
+		StubMappingScope scope = mainIndex.createScope();
+
+		String fieldPath = getFieldPath( fieldStructure );
+
+		Comparator<Double> comparator = Comparator.nullsLast( Comparable::compareTo );
+		var projection = scope.projection().distance( fieldPath, CENTER_POINT_1 )
+				.sortedSet( comparator ).toProjection();
+
+		var query = scope.query()
+				// Do NOT add any additional projection here: this serves as a non-regression test for HSEARCH-3618
+				.select( projection )
+				.where( f -> f.matchAll() );
+		addParameter( query, "center-param", CENTER_POINT_1 );
+
+		assertThatQuery( query.routing( dataSet.routingKey ).toQuery() )
+				.hits().asIs()
+				.usingElementComparator( TestComparators.lexicographic( APPROX_M_COMPARATOR ) )
+				.containsExactlyInAnyOrder(
+						new TreeSet<>( Set.of( dataSet.getFieldDistanceFromCenter1( 1 ) ) ),
+						new TreeSet<>( Set.of( dataSet.getFieldDistanceFromCenter1( 2 ) ) ),
+						new TreeSet<>( Set.of( dataSet.getFieldDistanceFromCenter1( 3 ) ) ),
+						TckConfiguration.get().getBackendFeatures()
+								.accumulatedNullValue( ProjectionCollector.sortedSet( comparator ) ) // Empty document
+				);
+	}
+
+	@ParameterizedTest(name = "{0}")
+	@MethodSource("params")
+	void array(TestedFieldStructure fieldStructure, DataSet dataSet) {
+		StubMappingScope scope = mainIndex.createScope();
+
+		String fieldPath = getFieldPath( fieldStructure );
+
+		var projection = scope.projection().distance( fieldPath, CENTER_POINT_1 ).array( Double.class ).toProjection();
+
+		var query = scope.query()
+				// Do NOT add any additional projection here: this serves as a non-regression test for HSEARCH-3618
+				.select( projection )
+				.where( f -> f.matchAll() );
+		addParameter( query, "center-param", CENTER_POINT_1 );
+
+		assertThatQuery( query.routing( dataSet.routingKey ).toQuery() )
+				.hits().asIs()
+				.usingElementComparator( TestComparators.array( APPROX_M_COMPARATOR ) )
+				.containsExactlyInAnyOrder(
+						new Double[] { dataSet.getFieldDistanceFromCenter1( 1 ) },
+						new Double[] { dataSet.getFieldDistanceFromCenter1( 2 ) },
+						new Double[] { dataSet.getFieldDistanceFromCenter1( 3 ) },
+						TckConfiguration.get().getBackendFeatures()
+								.accumulatedNullValue( ProjectionCollector.array( Double.class ) ) // Empty document
+				);
+	}
 
 	@Override
 	protected void addParameter(SearchQueryOptionsStep<?, ?, ?, ?, ?> query, String parameterName, Object value) {
@@ -37,7 +160,7 @@ protected DistanceToFieldProjectionValueStep<?, Double> distance(
 	protected ProjectionFinalStep<List<Double>> distanceMulti(
 			SearchProjectionFactory<EntityReference, DocumentReference> projection, String path, GeoPoint center,
 			String parameterName) {
-		return projection.distance( path, center ).multi();
+		return projection.distance( path, center ).list();
 	}
 
 	@Override
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionTypeCheckingAndConversionIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionTypeCheckingAndConversionIT.java
index c2fc1c30399..2837d2f0837 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionTypeCheckingAndConversionIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/DistanceProjectionTypeCheckingAndConversionIT.java
@@ -92,7 +92,7 @@ void multiValuedField_singleValuedProjection() {
 				.hasMessageContainingAll(
 						"Invalid cardinality for projection on field '" + fieldPath + "'",
 						"the projection is single-valued, but this field is multi-valued",
-						"Make sure to call '.multi()' when you create the projection"
+						"Make sure to call '.collector(...)' when you create the projection"
 				);
 	}
 
@@ -110,7 +110,7 @@ void singleValuedFieldInMultiValuedObjectField_flattened_singleValuedProjection(
 				.hasMessageContaining(
 						"Invalid cardinality for projection on field '" + fieldPath + "'",
 						"the projection is single-valued, but this field is multi-valued",
-						"Make sure to call '.multi()' when you create the projection"
+						"Make sure to call '.collector(...)' when you create the projection"
 				);
 	}
 
@@ -128,7 +128,7 @@ void singleValuedFieldInMultiValuedObjectField_nested_singleValuedProjection() {
 				.hasMessageContaining(
 						"Invalid cardinality for projection on field '" + fieldPath + "'",
 						"the projection is single-valued, but this field is multi-valued",
-						"Make sure to call '.multi()' when you create the projection"
+						"Make sure to call '.collector(...)' when you create the projection"
 				);
 	}
 
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/EntityProjectionIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/EntityProjectionIT.java
index ad8e0fb0b49..6d85f087109 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/EntityProjectionIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/EntityProjectionIT.java
@@ -21,6 +21,7 @@
 import org.hibernate.search.engine.common.EntityReference;
 import org.hibernate.search.engine.search.loading.spi.ProjectionHitMapper;
 import org.hibernate.search.engine.search.loading.spi.SearchLoadingContext;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.definition.spi.CompositeProjectionDefinition;
 import org.hibernate.search.engine.search.projection.definition.spi.ProjectionRegistry;
 import org.hibernate.search.engine.search.query.SearchQuery;
@@ -122,7 +123,7 @@ void projectionRegistryFallback_noLoadingAvailable_withProjectionRegistryEntry_i
 							.select( f -> f.composite().from(
 									f.object( binding.nested.absolutePath )
 											.from( f.field( binding.nested.fieldPath(), String.class ) )
-											.asList().multi(),
+											.asList().collector( ProjectionCollector.list() ),
 									f.entity()
 							).asList()
 							)
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionBaseIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionBaseIT.java
index 7eaeba53010..986ad72eba9 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionBaseIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionBaseIT.java
@@ -11,6 +11,7 @@
 
 import org.hibernate.search.engine.backend.types.ObjectStructure;
 import org.hibernate.search.engine.backend.types.dsl.SearchableProjectableIndexFieldTypeOptionsStep;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.dsl.ProjectionFinalStep;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
 import org.hibernate.search.integrationtest.backend.tck.testsupport.types.FieldTypeDescriptor;
@@ -143,7 +144,7 @@ protected ProjectionFinalStep<F> singleValuedProjection(SearchProjectionFactory<
 		@Override
 		protected ProjectionFinalStep<List<F>> multiValuedProjection(SearchProjectionFactory<?, ?> f,
 				String absoluteFieldPath, DataSet<F, F, FieldProjectionTestValues<F>> dataSet) {
-			return f.field( absoluteFieldPath, dataSet.fieldType.getJavaType() ).multi();
+			return f.field( absoluteFieldPath, dataSet.fieldType.getJavaType() ).collector( ProjectionCollector.list() );
 		}
 
 	}
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionMultiValuedBaseIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionMultiValuedBaseIT.java
index 50bf4db0aac..9a71ae593cd 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionMultiValuedBaseIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionMultiValuedBaseIT.java
@@ -6,11 +6,17 @@
 
 import static org.hibernate.search.util.impl.integrationtest.common.assertion.SearchResultAssert.assertThatQuery;
 import static org.hibernate.search.util.impl.integrationtest.mapper.stub.StubMapperUtils.documentProvider;
+import static org.junit.jupiter.api.Assumptions.assumeTrue;
 
+import java.lang.reflect.Array;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.Comparator;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Objects;
+import java.util.TreeSet;
 import java.util.function.Function;
 
 import org.hibernate.search.engine.backend.document.model.dsl.IndexSchemaElement;
@@ -88,6 +94,7 @@ static void setup() {
 		indexer.join();
 	}
 
+	@Deprecated
 	@ParameterizedTest(name = "{0} - {1}")
 	@MethodSource("params")
 	void simple(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> fieldType, DataSet<F> dataSet) {
@@ -108,6 +115,69 @@ void simple(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> field
 				);
 	}
 
+	@ParameterizedTest(name = "{0} - {1}")
+	@MethodSource("params")
+	void simpleList(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> fieldType, DataSet<F> dataSet) {
+		StubMappingScope scope = index.createScope();
+
+		String fieldPath = getFieldPath( fieldStructure, fieldType );
+
+		assertThatQuery( scope.query()
+				.select( f -> f.field( fieldPath, fieldType.getJavaType() ).list() )
+				.where( f -> f.matchAll() )
+				.routing( dataSet.routingKey )
+				.toQuery() )
+				.hasHitsAnyOrder(
+						dataSet.getFieldValues( 1 ),
+						dataSet.getFieldValues( 2 ),
+						dataSet.getFieldValues( 3 ),
+						Collections.emptyList() // Empty document
+				);
+	}
+
+	@ParameterizedTest(name = "{0} - {1}")
+	@MethodSource("params")
+	void simpleSet(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> fieldType, DataSet<F> dataSet) {
+		StubMappingScope scope = index.createScope();
+
+		String fieldPath = getFieldPath( fieldStructure, fieldType );
+
+		assertThatQuery( scope.query()
+				.select( f -> f.field( fieldPath, fieldType.getJavaType() ).set() )
+				.where( f -> f.matchAll() )
+				.routing( dataSet.routingKey )
+				.toQuery() )
+				.hasHitsAnyOrder(
+						new HashSet<>( dataSet.getFieldValues( 1 ) ),
+						new HashSet<>( dataSet.getFieldValues( 2 ) ),
+						new HashSet<>( dataSet.getFieldValues( 3 ) ),
+						Collections.emptySet() // Empty document
+				);
+	}
+
+	@SuppressWarnings("unchecked")
+	@ParameterizedTest(name = "{0} - {1}")
+	@MethodSource("params")
+	void simpleArray(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> fieldType, DataSet<F> dataSet) {
+		StubMappingScope scope = index.createScope();
+
+		String fieldPath = getFieldPath( fieldStructure, fieldType );
+
+		assertThatQuery( scope.query()
+				.select( f -> f.field( fieldPath, fieldType.getJavaType() )
+						.array( fieldType.getJavaType() ) )
+				.where( f -> f.matchAll() )
+				.routing( dataSet.routingKey )
+				.toQuery() )
+				.hasHitsAnyOrder(
+						dataSet.getFieldValues( 1 ).toArray( n -> (F[]) Array.newInstance( fieldType.getJavaType(), n ) ),
+						dataSet.getFieldValues( 2 ).toArray( n -> (F[]) Array.newInstance( fieldType.getJavaType(), n ) ),
+						dataSet.getFieldValues( 3 ).toArray( n -> (F[]) Array.newInstance( fieldType.getJavaType(), n ) ),
+						(F[]) Array.newInstance( fieldType.getJavaType(), 0 ) // Empty document
+				);
+
+	}
+
 	@ParameterizedTest(name = "{0} - {1}")
 	@MethodSource("params")
 	void noClass(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> fieldType, DataSet<F> dataSet) {
@@ -116,7 +186,7 @@ void noClass(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> fiel
 		String fieldPath = getFieldPath( fieldStructure, fieldType );
 
 		assertThatQuery( scope.query()
-				.select( f -> f.field( fieldPath ).multi() )
+				.select( f -> f.field( fieldPath ).list() )
 				.where( f -> f.matchAll() )
 				.routing( dataSet.routingKey )
 				.toQuery() )
@@ -140,8 +210,8 @@ void duplicated(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> f
 
 		assertThatQuery( scope.query()
 				.select( f -> f.composite(
-						f.field( fieldPath, fieldType.getJavaType() ).multi(),
-						f.field( fieldPath, fieldType.getJavaType() ).multi()
+						f.field( fieldPath, fieldType.getJavaType() ).list(),
+						f.field( fieldPath, fieldType.getJavaType() ).list()
 				)
 				)
 				.where( f -> f.matchAll() )
@@ -155,6 +225,134 @@ void duplicated(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> f
 				);
 	}
 
+	@ParameterizedTest(name = "{0} - {1}")
+	@MethodSource("params")
+	void set(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> fieldType, DataSet<F> dataSet) {
+		StubMappingScope scope = index.createScope();
+
+		String fieldPath = getFieldPath( fieldStructure, fieldType );
+
+		var multi = scope.projection().field( fieldPath, fieldType.getJavaType() )
+				.set()
+				.toProjection();
+
+		assertThatQuery( scope.query()
+				.select( multi )
+				.where( f -> f.matchAll() )
+				.routing( dataSet.routingKey )
+				.toQuery() )
+				.hasHitsAnyOrder(
+						new HashSet<>( dataSet.getFieldValues( 1 ) ),
+						new HashSet<>( dataSet.getFieldValues( 2 ) ),
+						new HashSet<>( dataSet.getFieldValues( 3 ) ),
+						Collections.emptySet() // Empty document
+				);
+	}
+
+	@ParameterizedTest(name = "{0} - {1}")
+	@MethodSource("params")
+	void sortedSet(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> fieldType, DataSet<F> dataSet) {
+		assumeTrue( Comparable.class.isAssignableFrom( fieldType.getJavaType() ),
+				"Some types that cannot be compared will fail the test as they cannot be added to a set without a comparator defined" );
+
+		StubMappingScope scope = index.createScope();
+
+		String fieldPath = getFieldPath( fieldStructure, fieldType );
+
+		var multi = scope.projection().field( fieldPath, fieldType.getJavaType() )
+				.sortedSet()
+				.toProjection();
+
+		assertThatQuery( scope.query()
+				.select( multi )
+				.where( f -> f.matchAll() )
+				.routing( dataSet.routingKey )
+				.toQuery() )
+				.hasHitsAnyOrder(
+						new TreeSet<>( dataSet.getFieldValues( 1 ) ),
+						new TreeSet<>( dataSet.getFieldValues( 2 ) ),
+						new TreeSet<>( dataSet.getFieldValues( 3 ) ),
+						Collections.emptySortedSet() // Empty document
+				);
+	}
+
+	@ParameterizedTest(name = "{0} - {1}")
+	@MethodSource("params")
+	void sortedSetComparator(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> fieldType, DataSet<F> dataSet) {
+		StubMappingScope scope = index.createScope();
+
+		String fieldPath = getFieldPath( fieldStructure, fieldType );
+
+		Comparator<F> comparator = Comparator.comparing( Objects::toString );
+		var multi = scope.projection().field( fieldPath, fieldType.getJavaType() )
+				.sortedSet( comparator )
+				.toProjection();
+
+		assertThatQuery( scope.query()
+				.select( multi )
+				.where( f -> f.matchAll() )
+				.routing( dataSet.routingKey )
+				.toQuery() )
+				.hasHitsAnyOrder(
+						treeSet( comparator, dataSet.getFieldValues( 1 ) ),
+						treeSet( comparator, dataSet.getFieldValues( 2 ) ),
+						treeSet( comparator, dataSet.getFieldValues( 3 ) ),
+						Collections.emptySortedSet() // Empty document
+				);
+	}
+
+	private static <F> TreeSet<F> treeSet(Comparator<F> comparator, List<F> values) {
+		TreeSet<F> set = new TreeSet<>( comparator );
+		set.addAll( values );
+		return set;
+	}
+
+	@SuppressWarnings("unchecked")
+	@ParameterizedTest(name = "{0} - {1}")
+	@MethodSource("params")
+	void array(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> fieldType, DataSet<F> dataSet) {
+		StubMappingScope scope = index.createScope();
+
+		String fieldPath = getFieldPath( fieldStructure, fieldType );
+
+		var multi = scope.projection().field( fieldPath, fieldType.getJavaType() )
+				.array( fieldType.getJavaType() )
+				.toProjection();
+
+		F[] arrayToConvert = (F[]) Array.newInstance( fieldType.getJavaType(), 0 );
+		assertThatQuery( scope.query()
+				.select( multi )
+				.where( f -> f.matchAll() )
+				.routing( dataSet.routingKey )
+				.toQuery() )
+				.hasHitsAnyOrder(
+						dataSet.getFieldValues( 1 ).toArray( arrayToConvert ),
+						dataSet.getFieldValues( 2 ).toArray( arrayToConvert ),
+						dataSet.getFieldValues( 3 ).toArray( arrayToConvert ),
+						arrayToConvert // Empty document
+				);
+	}
+
+	@ParameterizedTest(name = "{0} - {1}")
+	@MethodSource("params")
+	void explicitList(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> fieldType, DataSet<F> dataSet) {
+		StubMappingScope scope = index.createScope();
+
+		String fieldPath = getFieldPath( fieldStructure, fieldType );
+
+		assertThatQuery( scope.query()
+				.select( f -> f.field( fieldPath, fieldType.getJavaType() ).list() )
+				.where( f -> f.matchAll() )
+				.routing( dataSet.routingKey )
+				.toQuery() )
+				.hasHitsAnyOrder(
+						dataSet.getFieldValues( 1 ),
+						dataSet.getFieldValues( 2 ),
+						dataSet.getFieldValues( 3 ),
+						Collections.emptyList() // Empty document
+				);
+	}
+
 	private String getFieldPath(TestedFieldStructure fieldStructure, FieldTypeDescriptor<F, ?> fieldType) {
 		return index.binding().getFieldPath( fieldStructure, fieldType );
 	}
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionSingleValuedBaseIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionSingleValuedBaseIT.java
index 7344e381631..412e42eb625 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionSingleValuedBaseIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionSingleValuedBaseIT.java
@@ -4,6 +4,7 @@
  */
 package org.hibernate.search.integrationtest.backend.tck.search.projection;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.hibernate.search.util.impl.integrationtest.common.assertion.SearchResultAssert.assertThatQuery;
 import static org.hibernate.search.util.impl.integrationtest.mapper.stub.StubMapperUtils.documentProvider;
 import static org.junit.jupiter.api.Assumptions.assumeTrue;
@@ -12,6 +13,7 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.Optional;
 import java.util.function.Function;
 
 import org.hibernate.search.engine.backend.document.model.dsl.IndexSchemaElement;
@@ -111,6 +113,29 @@ void simple(TestedFieldStructure fieldStructure,
 				);
 	}
 
+	@ParameterizedTest(name = "{0} - {1}")
+	@MethodSource("params")
+	void optional(TestedFieldStructure fieldStructure,
+			FieldTypeDescriptor<F, ?> fieldType, DataSet<F> dataSet) {
+		StubMappingScope scope = index.createScope();
+
+		String fieldPath = getFieldPath( fieldStructure, fieldType );
+
+		assertThat( scope.query()
+				.select( f -> f.field( fieldPath, fieldType.getJavaType() ).optional() )
+				.where( f -> f.matchAll() )
+				.routing( dataSet.routingKey )
+				.toQuery()
+				.fetchAllHits() )
+				.usingRecursiveFieldByFieldElementComparator()
+				.contains(
+						Optional.of( dataSet.getFieldValue( 1 ) ),
+						Optional.of( dataSet.getFieldValue( 2 ) ),
+						Optional.of( dataSet.getFieldValue( 3 ) ),
+						Optional.empty() // Empty document
+				);
+	}
+
 	@ParameterizedTest(name = "{0} - {1}")
 	@MethodSource("params")
 	void noClass(TestedFieldStructure fieldStructure,
@@ -145,7 +170,7 @@ void multi(TestedFieldStructure fieldStructure,
 		String fieldPath = getFieldPath( fieldStructure, fieldType );
 
 		assertThatQuery( scope.query()
-				.select( f -> f.field( fieldPath, fieldType.getJavaType() ).multi() )
+				.select( f -> f.field( fieldPath, fieldType.getJavaType() ).list() )
 				.where( f -> f.matchAll() )
 				.routing( dataSet.routingKey )
 				.toQuery() )
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionTypeCheckingAndConversionIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionTypeCheckingAndConversionIT.java
index 533f45eb512..dd9643d08f2 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionTypeCheckingAndConversionIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/FieldProjectionTypeCheckingAndConversionIT.java
@@ -185,7 +185,7 @@ void multiValuedField_singleValuedProjection(FieldTypeDescriptor<F, ?> fieldType
 				.hasMessageContainingAll(
 						"Invalid cardinality for projection on field '" + fieldPath + "'",
 						"the projection is single-valued, but this field is multi-valued",
-						"Make sure to call '.multi()' when you create the projection"
+						"Make sure to call '.collector(...)' when you create the projection"
 				);
 	}
 
@@ -204,7 +204,7 @@ void singleValuedFieldInMultiValuedObjectField_flattened_singleValuedProjection(
 				.hasMessageContaining(
 						"Invalid cardinality for projection on field '" + fieldPath + "'",
 						"the projection is single-valued, but this field is multi-valued",
-						"Make sure to call '.multi()' when you create the projection"
+						"Make sure to call '.collector(...)' when you create the projection"
 				);
 	}
 
@@ -223,7 +223,7 @@ void singleValuedFieldInMultiValuedObjectField_nested_singleValuedProjection(Fie
 				.hasMessageContaining(
 						"Invalid cardinality for projection on field '" + fieldPath + "'",
 						"the projection is single-valued, but this field is multi-valued",
-						"Make sure to call '.multi()' when you create the projection"
+						"Make sure to call '.collector(...)' when you create the projection"
 				);
 	}
 
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/ObjectProjectionSpecificsIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/ObjectProjectionSpecificsIT.java
index fc6cacc3104..ac2651743f3 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/ObjectProjectionSpecificsIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/ObjectProjectionSpecificsIT.java
@@ -16,6 +16,7 @@
 import org.hibernate.search.engine.backend.document.model.dsl.IndexSchemaObjectField;
 import org.hibernate.search.engine.backend.types.ObjectStructure;
 import org.hibernate.search.engine.backend.types.Projectable;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
 import org.hibernate.search.integrationtest.backend.tck.testsupport.util.TckConfiguration;
 import org.hibernate.search.integrationtest.backend.tck.testsupport.util.extension.SearchSetupHelper;
@@ -88,10 +89,10 @@ void innerObjectProjectionOnFieldOutsideOuterObjectProjectionFieldTree() {
 								f.object( "level1" )
 										.from( f.field( "level1.field1" ) )
 										.asList()
-										.multi()
+										.collector( ProjectionCollector.list() )
 						)
 						.asList()
-						.multi() )
+						.collector( ProjectionCollector.list() ) )
 				.where( f -> f.matchAll() )
 				.toQuery() )
 				.isInstanceOf( SearchException.class )
@@ -132,7 +133,7 @@ void multiValuedObjectField_singleValuedObjectProjection() {
 				.hasMessageContainingAll(
 						"Invalid cardinality for projection on field 'level1'",
 						"the projection is single-valued, but this field is multi-valued",
-						"Make sure to call '.multi()' when you create the projection"
+						"Make sure to call '.collector(...)' when you create the projection"
 				);
 	}
 
@@ -151,9 +152,9 @@ void singleValuedObjectField_effectivelyMultiValuedInContext() {
 						"Invalid cardinality for projection on field 'level1WithSingleValuedLevel2.level2'",
 						"the projection is single-valued, but this field is effectively multi-valued in this context",
 						"because parent object field 'level1WithSingleValuedLevel2' is multi-valued",
-						"call '.multi()' when you create the projection on field 'level1WithSingleValuedLevel2.level2'",
+						"call '.collector(...)' when you create the projection on field 'level1WithSingleValuedLevel2.level2'",
 						"or wrap that projection in an object projection like this:"
-								+ " 'f.object(\"level1WithSingleValuedLevel2\").from(<the projection on field level1WithSingleValuedLevel2.level2>).as(...).multi()'."
+								+ " 'f.object(\"level1WithSingleValuedLevel2\").from(<the projection on field level1WithSingleValuedLevel2.level2>).as(...).collector(...)'."
 				);
 	}
 
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/UnsupportedNestingProjectionBaseIT.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/UnsupportedNestingProjectionBaseIT.java
index a27647ad8c2..9ee02c51925 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/UnsupportedNestingProjectionBaseIT.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/projection/UnsupportedNestingProjectionBaseIT.java
@@ -12,6 +12,7 @@
 import org.hibernate.search.engine.backend.document.model.dsl.IndexSchemaElement;
 import org.hibernate.search.engine.backend.document.model.dsl.IndexSchemaObjectField;
 import org.hibernate.search.engine.backend.types.ObjectStructure;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.integrationtest.backend.tck.testsupport.util.extension.SearchSetupHelper;
 import org.hibernate.search.util.common.SearchException;
 import org.hibernate.search.util.impl.integrationtest.mapper.stub.SimpleMappedIndex;
@@ -39,7 +40,7 @@ void id() {
 		assertThatThrownBy( () -> index.createScope().query()
 				.select( f -> f.object( "nested" ).from(
 						f.id()
-				).asList().multi()
+				).asList().collector( ProjectionCollector.list() )
 				)
 				.where( f -> f.matchAll() )
 				.toQuery()
@@ -56,7 +57,7 @@ void entity() {
 		assertThatThrownBy( () -> index.createScope().query()
 				.select( f -> f.object( "nested" ).from(
 						f.entity()
-				).asList().multi()
+				).asList().collector( ProjectionCollector.list() )
 				)
 				.where( f -> f.matchAll() )
 				.toQuery()
@@ -73,7 +74,7 @@ void entityReference() {
 		assertThatThrownBy( () -> index.createScope().query()
 				.select( f -> f.object( "nested" ).from(
 						f.entityReference()
-				).asList().multi()
+				).asList().collector( ProjectionCollector.list() )
 				)
 				.where( f -> f.matchAll() )
 				.toQuery()
@@ -90,7 +91,7 @@ void documentReference() {
 		assertThatThrownBy( () -> index.createScope().query()
 				.select( f -> f.object( "nested" ).from(
 						f.documentReference()
-				).asList().multi()
+				).asList().collector( ProjectionCollector.list() )
 				)
 				.where( f -> f.matchAll() )
 				.toQuery()
@@ -107,7 +108,7 @@ void score() {
 		assertThatThrownBy( () -> index.createScope().query()
 				.select( f -> f.object( "nested" ).from(
 						f.score()
-				).asList().multi()
+				).asList().collector( ProjectionCollector.list() )
 				)
 				.where( f -> f.matchAll() )
 				.toQuery()
diff --git a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/testsupport/util/TckBackendFeatures.java b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/testsupport/util/TckBackendFeatures.java
index 05bbeb8537e..df62b670195 100644
--- a/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/testsupport/util/TckBackendFeatures.java
+++ b/integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/testsupport/util/TckBackendFeatures.java
@@ -10,6 +10,7 @@
 
 import org.hibernate.search.engine.backend.types.ObjectStructure;
 import org.hibernate.search.engine.backend.types.VectorSimilarity;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.integrationtest.backend.tck.testsupport.types.FieldTypeDescriptor;
 import org.hibernate.search.util.impl.integrationtest.mapper.stub.StubMappingBackendFeatures;
 
@@ -221,4 +222,8 @@ public <F> Double toDoubleValue(FieldTypeDescriptor<F, ?> descriptor, F fieldVal
 	public <F> boolean rawAggregationProduceSensibleDoubleValue(FieldTypeDescriptor<F, ?> fFieldTypeDescriptor) {
 		return true;
 	}
+
+	public <U, R> R accumulatedNullValue(ProjectionCollector.Provider<U, R> collector) {
+		return collector.get().empty();
+	}
 }
diff --git a/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorFieldProjectionIT.java b/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorFieldProjectionIT.java
index 938153ae9f9..d78f57ba1b5 100644
--- a/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorFieldProjectionIT.java
+++ b/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorFieldProjectionIT.java
@@ -14,6 +14,7 @@
 import java.util.Set;
 
 import org.hibernate.search.engine.search.common.ValueModel;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.DocumentId;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.FieldProjection;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.FullTextField;
@@ -24,7 +25,6 @@
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.ProjectionConstructor;
 import org.hibernate.search.mapper.pojo.standalone.mapping.SearchMapping;
 import org.hibernate.search.util.common.SearchException;
-import org.hibernate.search.util.impl.integrationtest.common.reporting.FailureReportUtils;
 import org.hibernate.search.util.impl.integrationtest.mapper.pojo.standalone.StandalonePojoMappingSetupHelper;
 import org.hibernate.search.util.impl.test.annotation.TestForIssue;
 
@@ -580,8 +580,8 @@ public MyProjection(@FieldProjection List<String> text, @FieldProjection List<In
 				f -> f.composite()
 						.from(
 								dummyProjectionForEnclosingClassInstance( f ),
-								f.field( "text", String.class ).multi(),
-								f.field( "integer", Integer.class ).multi()
+								f.field( "text", String.class ).collector( ProjectionCollector.list() ),
+								f.field( "integer", Integer.class ).collector( ProjectionCollector.list() )
 						)
 						.asList(),
 				Arrays.asList(
@@ -631,8 +631,8 @@ public MyProjection(@FieldProjection Collection<String> text, @FieldProjection C
 				f -> f.composite()
 						.from(
 								dummyProjectionForEnclosingClassInstance( f ),
-								f.field( "text", String.class ).multi(),
-								f.field( "integer", Integer.class ).multi()
+								f.field( "text", String.class ).collector( ProjectionCollector.list() ),
+								f.field( "integer", Integer.class ).collector( ProjectionCollector.list() )
 						)
 						.asList(),
 				Arrays.asList(
@@ -682,8 +682,8 @@ public MyProjection(@FieldProjection Iterable<String> text, @FieldProjection Ite
 				f -> f.composite()
 						.from(
 								dummyProjectionForEnclosingClassInstance( f ),
-								f.field( "text", String.class ).multi(),
-								f.field( "integer", Integer.class ).multi()
+								f.field( "text", String.class ).collector( ProjectionCollector.list() ),
+								f.field( "integer", Integer.class ).collector( ProjectionCollector.list() )
 						)
 						.asList(),
 				Arrays.asList(
@@ -717,19 +717,33 @@ public MyProjection(@FieldProjection Set<String> text, @FieldProjection List<Int
 			}
 		}
 
-		assertThatThrownBy( () -> setupHelper.start()
+		backendMock.expectAnySchema( INDEX_NAME );
+		SearchMapping mapping = setupHelper.start()
 				.withAnnotatedTypes( MyProjection.class )
-				.setup( IndexedEntity.class ) )
-				.isInstanceOf( SearchException.class )
-				.satisfies( FailureReportUtils.hasFailureReport()
-						.typeContext( MyProjection.class.getName() )
-						.constructorContext( ProjectionConstructorFieldProjectionIT.class, Set.class, List.class )
-						.methodParameterContext( 1, "text" )
-						.failure( "Invalid parameter type for projection constructor",
-								"java.util.Set<java.lang.String>",
-								"When inferring the cardinality of inner projections from constructor parameters,"
-										+ " multi-valued constructor parameters must be lists (java.util.List<...>)"
-										+ " or list supertypes (java.lang.Iterable<...>, java.util.Collection<...>)" ) );
+				.setup( IndexedEntity.class );
+
+		testSuccessfulRootProjection(
+				mapping, IndexedEntity.class, MyProjection.class,
+				Arrays.asList(
+						Arrays.asList( Set.of( "result1_1", "result1_2" ), Arrays.asList( 11, 12 ) ),
+						Arrays.asList( Set.of( "result2_1" ), Arrays.asList( 21 ) ),
+						Arrays.asList( Set.of(), Collections.emptyList() ),
+						Arrays.asList( Set.of( "result4_1" ), Arrays.asList( 41 ) )
+				),
+				f -> f.composite()
+						.from(
+								dummyProjectionForEnclosingClassInstance( f ),
+								f.field( "text", String.class ).collector( ProjectionCollector.set() ),
+								f.field( "integer", Integer.class ).collector( ProjectionCollector.list() )
+						)
+						.asList(),
+				Arrays.asList(
+						new MyProjection( Set.of( "result1_1", "result1_2" ), Arrays.asList( 11, 12 ) ),
+						new MyProjection( Set.of( "result2_1" ), Arrays.asList( 21 ) ),
+						new MyProjection( Set.of(), Collections.emptyList() ),
+						new MyProjection( Set.of( "result4_1" ), Arrays.asList( 41 ) )
+				)
+		);
 	}
 
 }
diff --git a/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorHighlightProjectionIT.java b/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorHighlightProjectionIT.java
index 364689312ef..20587c4a440 100644
--- a/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorHighlightProjectionIT.java
+++ b/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorHighlightProjectionIT.java
@@ -12,6 +12,7 @@
 import java.util.List;
 import java.util.Set;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.DocumentId;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.FullTextField;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.GenericField;
@@ -236,7 +237,7 @@ public MyProjection(@HighlightProjection String text) {
 				f -> f.composite()
 						.from(
 								dummyProjectionForEnclosingClassInstance( f ),
-								f.highlight( "text" ).single()
+								f.highlight( "text" ).collector( ProjectionCollector.nullable() )
 						)
 						.asList(),
 				Arrays.asList(
@@ -422,16 +423,28 @@ public MyProjection(@HighlightProjection Set<String> text) {
 			}
 		}
 
-		assertThatThrownBy( () -> setupHelper.start()
+		backendMock.expectAnySchema( INDEX_NAME );
+		SearchMapping mapping = setupHelper.start()
 				.withAnnotatedTypes( MyProjection.class )
-				.setup( IndexedEntity.class ) )
-				.isInstanceOf( SearchException.class )
-				.satisfies( FailureReportUtils.hasFailureReport()
-						.typeContext( MyProjection.class.getName() )
-						.constructorContext( ProjectionConstructorHighlightProjectionIT.class, Set.class )
-						.methodParameterContext( 1, "text" )
-						.failure( "Invalid parameter type for projection constructor: java.util.Set<java.lang.String>",
-								"When inferring the cardinality of inner projections from constructor parameters, multi-valued constructor parameters must be lists (java.util.List<...>) or list supertypes (java.lang.Iterable<...>, java.util.Collection<...>)" ) );
+				.setup( IndexedEntity.class );
+
+		testSuccessfulRootProjection(
+				mapping, IndexedEntity.class, MyProjection.class,
+				Arrays.asList(
+						Arrays.asList( Arrays.asList( "result1_term1", "result1_term2" ) ),
+						Arrays.asList( Arrays.asList( "result1_term1" ) )
+				),
+				f -> f.composite()
+						.from(
+								dummyProjectionForEnclosingClassInstance( f ),
+								f.highlight( "text" )
+						)
+						.asList(),
+				Arrays.asList(
+						new MyProjection( Set.of( "result1_term1", "result1_term2" ) ),
+						new MyProjection( Set.of( "result1_term1" ) )
+				)
+		);
 	}
 
 	@Test
diff --git a/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorInnerInferredIT.java b/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorInnerInferredIT.java
index 1e06cffee73..626af40cd0b 100644
--- a/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorInnerInferredIT.java
+++ b/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorInnerInferredIT.java
@@ -4,8 +4,6 @@
  */
 package org.hibernate.search.integrationtest.mapper.pojo.mapping.definition;
 
-import static org.assertj.core.api.Assertions.assertThatThrownBy;
-
 import java.lang.invoke.MethodHandles;
 import java.util.Arrays;
 import java.util.Collection;
@@ -13,6 +11,7 @@
 import java.util.List;
 import java.util.Set;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.DocumentId;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.FullTextField;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.GenericField;
@@ -20,8 +19,6 @@
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.IndexedEmbedded;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.ProjectionConstructor;
 import org.hibernate.search.mapper.pojo.standalone.mapping.SearchMapping;
-import org.hibernate.search.util.common.SearchException;
-import org.hibernate.search.util.impl.integrationtest.common.reporting.FailureReportUtils;
 import org.hibernate.search.util.impl.integrationtest.mapper.pojo.standalone.StandalonePojoMappingSetupHelper;
 import org.hibernate.search.util.impl.test.annotation.TestForIssue;
 
@@ -120,8 +117,8 @@ public MyProjection(List<String> text, List<Integer> integer) {
 				f -> f.composite()
 						.from(
 								dummyProjectionForEnclosingClassInstance( f ),
-								f.field( "text", String.class ).multi(),
-								f.field( "integer", Integer.class ).multi()
+								f.field( "text", String.class ).collector( ProjectionCollector.list() ),
+								f.field( "integer", Integer.class ).collector( ProjectionCollector.list() )
 						)
 						.asList(),
 				Arrays.asList(
@@ -171,8 +168,8 @@ public MyProjection(Collection<String> text, Collection<Integer> integer) {
 				f -> f.composite()
 						.from(
 								dummyProjectionForEnclosingClassInstance( f ),
-								f.field( "text", String.class ).multi(),
-								f.field( "integer", Integer.class ).multi()
+								f.field( "text", String.class ).collector( ProjectionCollector.list() ),
+								f.field( "integer", Integer.class ).collector( ProjectionCollector.list() )
 						)
 						.asList(),
 				Arrays.asList(
@@ -222,8 +219,8 @@ public MyProjection(Iterable<String> text, Iterable<Integer> integer) {
 				f -> f.composite()
 						.from(
 								dummyProjectionForEnclosingClassInstance( f ),
-								f.field( "text", String.class ).multi(),
-								f.field( "integer", Integer.class ).multi()
+								f.field( "text", String.class ).collector( ProjectionCollector.list() ),
+								f.field( "integer", Integer.class ).collector( ProjectionCollector.list() )
 						)
 						.asList(),
 				Arrays.asList(
@@ -257,19 +254,33 @@ public MyProjection(Set<String> text, List<Integer> integer) {
 			}
 		}
 
-		assertThatThrownBy( () -> setupHelper.start()
+		backendMock.expectAnySchema( INDEX_NAME );
+		SearchMapping mapping = setupHelper.start()
 				.withAnnotatedTypes( MyProjection.class )
-				.setup( IndexedEntity.class ) )
-				.isInstanceOf( SearchException.class )
-				.satisfies( FailureReportUtils.hasFailureReport()
-						.typeContext( MyProjection.class.getName() )
-						.constructorContext( ProjectionConstructorInnerInferredIT.class, Set.class, List.class )
-						.methodParameterContext( 1, "text" )
-						.failure( "Invalid parameter type for projection constructor",
-								"java.util.Set<java.lang.String>",
-								"When inferring the cardinality of inner projections from constructor parameters,"
-										+ " multi-valued constructor parameters must be lists (java.util.List<...>)"
-										+ " or list supertypes (java.lang.Iterable<...>, java.util.Collection<...>)" ) );
+				.setup( IndexedEntity.class );
+
+		testSuccessfulRootProjection(
+				mapping, IndexedEntity.class, MyProjection.class,
+				Arrays.asList(
+						Arrays.asList( Set.of( "result1_1", "result1_2" ), Arrays.asList( 11, 12 ) ),
+						Arrays.asList( Set.of( "result2_1" ), Arrays.asList( 21 ) ),
+						Arrays.asList( Set.of(), Collections.emptyList() ),
+						Arrays.asList( Set.of( "result4_1" ), Arrays.asList( 41 ) )
+				),
+				f -> f.composite()
+						.from(
+								dummyProjectionForEnclosingClassInstance( f ),
+								f.field( "text", String.class ).collector( ProjectionCollector.set() ),
+								f.field( "integer", Integer.class ).collector( ProjectionCollector.list() )
+						)
+						.asList(),
+				Arrays.asList(
+						new MyProjection( Set.of( "result1_1", "result1_2" ), Arrays.asList( 11, 12 ) ),
+						new MyProjection( Set.of( "result2_1" ), Arrays.asList( 21 ) ),
+						new MyProjection( Set.of(), Collections.emptyList() ),
+						new MyProjection( Set.of( "result4_1" ), Arrays.asList( 41 ) )
+				)
+		);
 	}
 
 	@Test
@@ -493,7 +504,7 @@ public MyProjection(String text, List<MyInnerProjection> contained) {
 												f.field( "contained.integer", Integer.class )
 										)
 										.asList()
-										.multi()
+										.collector( ProjectionCollector.list() )
 						)
 						.asList(),
 				Arrays.asList(
@@ -583,7 +594,7 @@ public MyProjection(String text, Collection<MyInnerProjection> contained) {
 												f.field( "contained.integer", Integer.class )
 										)
 										.asList()
-										.multi()
+										.collector( ProjectionCollector.list() )
 						)
 						.asList(),
 				Arrays.asList(
@@ -673,7 +684,7 @@ public MyProjection(String text, Iterable<MyInnerProjection> contained) {
 												f.field( "contained.integer", Integer.class )
 										)
 										.asList()
-										.multi()
+										.collector( ProjectionCollector.list() )
 						)
 						.asList(),
 				Arrays.asList(
@@ -732,19 +743,54 @@ public MyProjection(String text, Set<MyInnerProjection> contained) {
 			}
 		}
 
-		assertThatThrownBy( () -> setupHelper.start()
-				.withAnnotatedTypes( MyProjection.class )
-				.setup( IndexedEntity.class ) )
-				.isInstanceOf( SearchException.class )
-				.satisfies( FailureReportUtils.hasFailureReport()
-						.typeContext( MyProjection.class.getName() )
-						.constructorContext( ProjectionConstructorInnerInferredIT.class, String.class, Set.class )
-						.methodParameterContext( 2, "contained" )
-						.failure( "Invalid parameter type for projection constructor",
-								"java.util.Set<" + MyInnerProjection.class.getName() + ">",
-								"When inferring the cardinality of inner projections from constructor parameters,"
-										+ " multi-valued constructor parameters must be lists (java.util.List<...>)"
-										+ " or list supertypes (java.lang.Iterable<...>, java.util.Collection<...>)" ) );
+		backendMock.expectAnySchema( INDEX_NAME );
+		SearchMapping mapping = setupHelper.start()
+				.withAnnotatedTypes( MyProjection.class, MyInnerProjection.class )
+				.setup( IndexedEntity.class );
+
+		testSuccessfulRootProjection(
+				mapping, IndexedEntity.class, MyProjection.class,
+				Arrays.asList(
+						Arrays.asList( "result1", Set.of(
+								Arrays.asList( "result1_1", 11 ),
+								Arrays.asList( "result1_2", 12 )
+						) ),
+						Arrays.asList( "result2", Set.of(
+								Arrays.asList( "result2_1", 21 )
+						) ),
+						Arrays.asList( "result3", Set.of() ),
+						Arrays.asList( "result4", Set.of(
+								Arrays.asList( "result4_1", 41 )
+						) )
+				),
+				f -> f.composite()
+						.from(
+								dummyProjectionForEnclosingClassInstance( f ),
+								f.field( "text", String.class ),
+								f.object( "contained" )
+										.from(
+												dummyProjectionForEnclosingClassInstance( f ),
+												f.field( "contained.text", String.class ),
+												f.field( "contained.integer", Integer.class )
+										)
+										.asList()
+										.collector( ProjectionCollector.set() )
+						)
+						.asList(),
+				Arrays.asList(
+						new MyProjection( "result1", Set.of(
+								new MyInnerProjection( "result1_1", 11 ),
+								new MyInnerProjection( "result1_2", 12 )
+						) ),
+						new MyProjection( "result2", Set.of(
+								new MyInnerProjection( "result2_1", 21 )
+						) ),
+						new MyProjection( "result3", Set.of() ),
+						new MyProjection( "result4", Set.of(
+								new MyInnerProjection( "result4_1", 41 )
+						) )
+				)
+		);
 	}
 
 }
diff --git a/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorObjectProjectionIT.java b/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorObjectProjectionIT.java
index 07d5a2669a0..43d7f2da1c8 100644
--- a/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorObjectProjectionIT.java
+++ b/integrationtest/mapper/pojo-base/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/mapping/definition/ProjectionConstructorObjectProjectionIT.java
@@ -13,6 +13,7 @@
 import java.util.List;
 import java.util.Set;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.DocumentId;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.FullTextField;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.GenericField;
@@ -705,7 +706,7 @@ public MyProjection(String text, @ObjectProjection List<MyInnerProjection> conta
 												f.field( "contained.integer", Integer.class )
 										)
 										.asList()
-										.multi()
+										.collector( ProjectionCollector.list() )
 						)
 						.asList(),
 				Arrays.asList(
@@ -795,7 +796,7 @@ public MyProjection(String text, @ObjectProjection Collection<MyInnerProjection>
 												f.field( "contained.integer", Integer.class )
 										)
 										.asList()
-										.multi()
+										.collector( ProjectionCollector.list() )
 						)
 						.asList(),
 				Arrays.asList(
@@ -885,7 +886,7 @@ public MyProjection(String text, @ObjectProjection Iterable<MyInnerProjection> c
 												f.field( "contained.integer", Integer.class )
 										)
 										.asList()
-										.multi()
+										.collector( ProjectionCollector.list() )
 						)
 						.asList(),
 				Arrays.asList(
@@ -944,18 +945,53 @@ public MyProjection(String text, @ObjectProjection Set<MyInnerProjection> contai
 			}
 		}
 
-		assertThatThrownBy( () -> setupHelper.start()
-				.withAnnotatedTypes( MyProjection.class )
-				.setup( IndexedEntity.class ) )
-				.isInstanceOf( SearchException.class )
-				.satisfies( FailureReportUtils.hasFailureReport()
-						.typeContext( MyProjection.class.getName() )
-						.constructorContext( ProjectionConstructorObjectProjectionIT.class, String.class, Set.class )
-						.methodParameterContext( 2, "contained" )
-						.failure( "Invalid parameter type for projection constructor",
-								"java.util.Set<" + MyInnerProjection.class.getName() + ">",
-								"When inferring the cardinality of inner projections from constructor parameters,"
-										+ " multi-valued constructor parameters must be lists (java.util.List<...>)"
-										+ " or list supertypes (java.lang.Iterable<...>, java.util.Collection<...>)" ) );
+		backendMock.expectAnySchema( INDEX_NAME );
+		SearchMapping mapping = setupHelper.start()
+				.withAnnotatedTypes( MyProjection.class, MyInnerProjection.class )
+				.setup( IndexedEntity.class );
+
+		testSuccessfulRootProjection(
+				mapping, IndexedEntity.class, MyProjection.class,
+				Arrays.asList(
+						Arrays.asList( "result1", Arrays.asList(
+								Arrays.asList( "result1_1", 11 ),
+								Arrays.asList( "result1_2", 12 )
+						) ),
+						Arrays.asList( "result2", Arrays.asList(
+								Arrays.asList( "result2_1", 21 )
+						) ),
+						Arrays.asList( "result3", Collections.emptyList() ),
+						Arrays.asList( "result4", Arrays.asList(
+								Arrays.asList( "result4_1", 41 )
+						) )
+				),
+				f -> f.composite()
+						.from(
+								dummyProjectionForEnclosingClassInstance( f ),
+								f.field( "text", String.class ),
+								f.object( "contained" )
+										.from(
+												dummyProjectionForEnclosingClassInstance( f ),
+												f.field( "contained.text", String.class ),
+												f.field( "contained.integer", Integer.class )
+										)
+										.asList()
+										.collector( ProjectionCollector.set() )
+						)
+						.asList(),
+				Arrays.asList(
+						new MyProjection( "result1", Set.of(
+								new MyInnerProjection( "result1_1", 11 ),
+								new MyInnerProjection( "result1_2", 12 )
+						) ),
+						new MyProjection( "result2", Set.of(
+								new MyInnerProjection( "result2_1", 21 )
+						) ),
+						new MyProjection( "result3", Set.of() ),
+						new MyProjection( "result4", Set.of(
+								new MyInnerProjection( "result4_1", 41 )
+						) )
+				)
+		);
 	}
 }
diff --git a/integrationtest/mapper/pojo-standalone-realbackend/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/standalone/realbackend/mapping/ProjectionConstructorDistanceProjectionIT.java b/integrationtest/mapper/pojo-standalone-realbackend/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/standalone/realbackend/mapping/ProjectionConstructorDistanceProjectionIT.java
index 99bffd5d9a2..828f71ea77d 100644
--- a/integrationtest/mapper/pojo-standalone-realbackend/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/standalone/realbackend/mapping/ProjectionConstructorDistanceProjectionIT.java
+++ b/integrationtest/mapper/pojo-standalone-realbackend/src/test/java/org/hibernate/search/integrationtest/mapper/pojo/standalone/realbackend/mapping/ProjectionConstructorDistanceProjectionIT.java
@@ -337,6 +337,6 @@ public MyProjection(@DistanceProjection(fromParam = "param", path = "points") Li
 				.setup( IndexedEntity.class )
 		).isInstanceOf( SearchException.class )
 				.hasMessageContainingAll(
-						"Invalid constructor parameter type: 'java.lang.String'. The distance projection results in values of type 'List<Double>'" );
+						"Invalid constructor parameter type: 'java.lang.String'. The distance projection results in values of type 'SomeContainer<Double>'" );
 	}
 }
diff --git a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/logging/impl/Log.java b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/logging/impl/Log.java
index 52bca587bd9..239b1915eb2 100644
--- a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/logging/impl/Log.java
+++ b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/logging/impl/Log.java
@@ -705,8 +705,9 @@ SearchException invalidAbstractTypeForProjectionConstructor(
 	@Message(id = ID_OFFSET + 115,
 			value = "Invalid parameter type for projection constructor: %1$s."
 					+ " When inferring the cardinality of inner projections from constructor parameters,"
-					+ " multi-valued constructor parameters must be lists (java.util.List<...>)"
-					+ " or list supertypes (java.lang.Iterable<...>, java.util.Collection<...>)")
+					+ " multi-valued constructor parameters must be lists/sets (java.util.List<...>/java.util.Set<...>/java.util.SortedSet<...>)"
+					+ ", their supertypes (java.lang.Iterable<...>, java.util.Collection<...>)"
+					+ " or arrays")
 	SearchException invalidMultiValuedParameterTypeForProjectionConstructor(
 			@FormatWith(PojoTypeModelFormatter.class) PojoTypeModel<?> parentTypeModel);
 
@@ -1046,4 +1047,10 @@ void indexingProgressWithRemainingTime(float estimatePercentileComplete, long do
 	@Message(id = ID_OFFSET + 169,
 			value = "Mass indexing is going to index approx. %1$d entities (%2$s). Actual number may change once the indexing starts.")
 	void indexingEntitiesApprox(long count, String types);
+
+	@Message(id = ID_OFFSET + 170,
+			value = "Implicit binding of a java.util.SortedSet<%1$s> constructor parameter is not possible since %1$s is not implementing java.lang.Comparable."
+					+ " Either make %1$s implement java.lang.Comparable or create a custom @ProjectionBinding and use the ProjectionCollector.sortedSet(comparator) collector provider in it.")
+	SearchException cannotBindSortedSetWithNonComparableElements(@FormatWith(ClassFormatter.class) Class<?> elementType,
+			@Param EventContext eventContext);
 }
diff --git a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/ProjectionBindingContext.java b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/ProjectionBindingContext.java
index 593da93a6bf..18748bca436 100644
--- a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/ProjectionBindingContext.java
+++ b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/ProjectionBindingContext.java
@@ -12,11 +12,14 @@
 import org.hibernate.search.engine.environment.bean.BeanHolder;
 import org.hibernate.search.engine.environment.bean.BeanReference;
 import org.hibernate.search.engine.environment.bean.BeanResolver;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+import org.hibernate.search.engine.search.projection.ProjectionCollectorProviderFactory;
 import org.hibernate.search.engine.search.projection.definition.ProjectionDefinition;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
 import org.hibernate.search.mapper.pojo.bridge.mapping.annotation.PropertyBinderRef;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.ObjectProjection;
 import org.hibernate.search.mapper.pojo.model.PojoModelConstructorParameter;
+import org.hibernate.search.mapper.pojo.model.PojoModelValue;
 import org.hibernate.search.util.common.SearchException;
 import org.hibernate.search.util.common.annotation.Incubating;
 
@@ -35,9 +38,12 @@ public interface ProjectionBindingContext {
 	 * Hibernate Search will check that these expectations are met, and throw an exception if they are not.
 	 * @param definition A definition of the projection
 	 * to bind to the {@link #constructorParameter()}.
-	 * @param <P> The type of values returned by the projection.
+	 * @param <P> The type of single projected value.
+	 * @param <C> The type of values returned by the projection.
+	 * It may be the same as {@code P}, if it is a simple single-valued projection,
+	 * or a type of the container if the {@code P} values are wrapped in some type of container (e.g. {@code Optional<..>}, {@code Collection<..>}..).
 	 */
-	<P> void definition(Class<P> expectedValueType, ProjectionDefinition<? extends P> definition);
+	<P, C> void definition(Class<P> expectedValueType, ProjectionDefinition<? extends C> definition);
 
 	/**
 	 * Binds the {@link #constructorParameter()} to the given projection definition.
@@ -47,9 +53,13 @@ public interface ProjectionBindingContext {
 	 * Hibernate Search will check that these expectations are met, and throw an exception if they are not.
 	 * @param definitionHolder A {@link BeanHolder} containing the definition of the projection
 	 * to bind to the {@link #constructorParameter()}.
-	 * @param <P> The type of values returned by the projection.
+	 * @param <P> The type of single projected value.
+	 * @param <C> The type of values returned by the projection.
+	 * It may be the same as {@code P}, if it is a simple single-valued projection,
+	 * or a type of the container if the {@code P} values are wrapped in some type of container (e.g. {@code Optional<..>}, {@code Collection<..>}..).
 	 */
-	<P> void definition(Class<P> expectedValueType, BeanHolder<? extends ProjectionDefinition<? extends P>> definitionHolder);
+	<P, C> void definition(Class<P> expectedValueType,
+			BeanHolder<? extends ProjectionDefinition<? extends C>> definitionHolder);
 
 	/**
 	 * Inspects the type of the {@link #constructorParameter()}
@@ -58,7 +68,9 @@ public interface ProjectionBindingContext {
 	 * @return An optional containing a context that can be used to bind a projection
 	 * if the type of the {@link #constructorParameter()} can be bound to a multi-valued projection;
 	 * an empty optional otherwise.
+	 * @deprecated Use {@link #containerElement()} and various bind methods of this context instead.
 	 */
+	@Deprecated(since = "8.0")
 	@Incubating
 	Optional<? extends ProjectionBindingMultiContext> multi();
 
@@ -74,6 +86,14 @@ public interface ProjectionBindingContext {
 	@Incubating
 	PojoModelConstructorParameter constructorParameter();
 
+	/**
+	 * @return An entry point allowing to inspect the constructor parameter container element being bound to a projection.
+	 * Returns non-empty optional only if a {@link #constructorParameter()} can be bound to a container-wrapped projection
+	 * (be it a single-valued optional, or some multi-valued collection).
+	 */
+	@Incubating
+	Optional<PojoModelValue<?>> containerElement();
+
 	/**
 	 * @param name The name of the parameter.
 	 * @return The value provided for this parameter.
@@ -135,8 +155,10 @@ default Optional<Object> paramOptional(String name) {
 	 * @see org.hibernate.search.engine.search.projection.dsl.CompositeProjectionInnerStep#as(Class)
 	 */
 	@Incubating
-	<T> BeanHolder<? extends ProjectionDefinition<T>> createObjectDefinition(String fieldPath, Class<T> projectedType,
-			TreeFilterDefinition filter);
+	default <T> BeanHolder<? extends ProjectionDefinition<T>> createObjectDefinition(String fieldPath, Class<T> projectedType,
+			TreeFilterDefinition filter) {
+		return createObjectDefinition( fieldPath, projectedType, filter, ProjectionCollector.nullable() );
+	}
 
 	/**
 	 * @param fieldPath The (relative) path to an object field in the indexed document.
@@ -149,10 +171,30 @@ <T> BeanHolder<? extends ProjectionDefinition<T>> createObjectDefinition(String
 	 * @throws SearchException If mapping the given type to a projection definition fails.
 	 * @see org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory#object(String)
 	 * @see org.hibernate.search.engine.search.projection.dsl.CompositeProjectionInnerStep#as(Class)
+	 * @deprecated Use {@link #createObjectDefinition(String, Class, TreeFilterDefinition, ProjectionCollector.Provider)} instead.
 	 */
+	@Deprecated(since = "8.0")
 	@Incubating
-	<T> BeanHolder<? extends ProjectionDefinition<List<T>>> createObjectDefinitionMulti(String fieldPath,
-			Class<T> projectedType, TreeFilterDefinition filter);
+	default <T> BeanHolder<? extends ProjectionDefinition<List<T>>> createObjectDefinitionMulti(String fieldPath,
+			Class<T> projectedType, TreeFilterDefinition filter) {
+		return createObjectDefinition( fieldPath, projectedType, filter, ProjectionCollector.list() );
+	}
+
+	/**
+	 * @param fieldPath The (relative) path to an object field in the indexed document.
+	 * @param projectedType A type expected to have a corresponding projection mapping
+	 * (e.g. using {@link org.hibernate.search.mapper.pojo.mapping.definition.annotation.ProjectionConstructor}).
+	 * @param filter The filter to apply to determine which nested index field projections should be included in the projection.
+	 * See {@link ObjectProjection#includePaths()}, {@link ObjectProjection#excludePaths()},
+	 * {@link ObjectProjection#includeDepth()}, ...
+	 * @return A container-wrapped object projection definition for the given type.
+	 * @throws SearchException If mapping the given type to a projection definition fails.
+	 * @see org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory#object(String)
+	 * @see org.hibernate.search.engine.search.projection.dsl.CompositeProjectionInnerStep#as(Class)
+	 */
+	@Incubating
+	<C, T> BeanHolder<? extends ProjectionDefinition<C>> createObjectDefinition(String fieldPath,
+			Class<T> projectedType, TreeFilterDefinition filter, ProjectionCollector.Provider<T, C> collector);
 
 	/**
 	 * @param projectedType A type expected to have a corresponding projection mapping
@@ -177,4 +219,11 @@ <T> BeanHolder<? extends ProjectionDefinition<List<T>>> createObjectDefinitionMu
 	 */
 	boolean isIncluded(String fieldPath);
 
+	/**
+	 * @return An instance of a projection collector provider factory capable of supplying a collector provider
+	 * based on a container and component types.
+	 */
+	@Incubating
+	ProjectionCollectorProviderFactory projectionCollectorProviderFactory();
+
 }
diff --git a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/ProjectionBindingMultiContext.java b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/ProjectionBindingMultiContext.java
index 5e1c43f2cdd..985fc958149 100644
--- a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/ProjectionBindingMultiContext.java
+++ b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/ProjectionBindingMultiContext.java
@@ -14,7 +14,9 @@
 /**
  * The context returned by {@link ProjectionBindingContext#multi()}.
  * @see ProjectionBindingContext#multi()
+ * @deprecated Use {@link ProjectionBindingContext}/{@link ProjectionBindingContext#containerElement()} instead.
  */
+@Deprecated(since = "8.0")
 @Incubating
 public interface ProjectionBindingMultiContext {
 
diff --git a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/DistanceProjectionBinder.java b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/DistanceProjectionBinder.java
index 12ec04e8bc2..febbc6c3a8a 100644
--- a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/DistanceProjectionBinder.java
+++ b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/DistanceProjectionBinder.java
@@ -9,6 +9,7 @@
 import java.util.function.Function;
 
 import org.hibernate.search.engine.environment.bean.BeanHolder;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.definition.spi.ConstantProjectionDefinition;
 import org.hibernate.search.engine.search.projection.definition.spi.DistanceProjectionDefinition;
 import org.hibernate.search.engine.search.projection.dsl.DistanceToFieldProjectionOptionsStep;
@@ -16,9 +17,9 @@
 import org.hibernate.search.engine.spatial.DistanceUnit;
 import org.hibernate.search.engine.spatial.GeoPoint;
 import org.hibernate.search.mapper.pojo.logging.impl.Log;
+import org.hibernate.search.mapper.pojo.model.PojoModelValue;
 import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBinder;
 import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBindingContext;
-import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBindingMultiContext;
 import org.hibernate.search.util.common.impl.Contracts;
 import org.hibernate.search.util.common.logging.impl.LoggerFactory;
 
@@ -94,35 +95,36 @@ public DistanceProjectionBinder unit(DistanceUnit unit) {
 	@Override
 	public void bind(ProjectionBindingContext context) {
 		Contracts.assertNotNullNorEmpty( parameterName, "parameterName" );
-		Optional<? extends ProjectionBindingMultiContext> multiOptional = context.multi();
+		Optional<PojoModelValue<?>> containerElementOptional = context.containerElement();
 		String fieldPath = fieldPathOrFail( context );
-		if ( multiOptional.isPresent() ) {
-			ProjectionBindingMultiContext multi = multiOptional.get();
-			if ( !multi.containerElement().rawType().isAssignableFrom( Double.class ) ) {
-				throw log.invalidParameterTypeForDistanceProjectionInProjectionConstructor( multi.containerElement().rawType(),
-						"List<Double>" );
+		Class<?> containerClass;
+		if ( containerElementOptional.isPresent() ) {
+			PojoModelValue<?> containerElement = containerElementOptional.get();
+			if ( !containerElement.rawType().isAssignableFrom( Double.class ) ) {
+				throw log.invalidParameterTypeForDistanceProjectionInProjectionConstructor(
+						containerElement.rawType(),
+						"SomeContainer<Double>" );
 			}
-			bind( context, multi, fieldPath );
+			containerClass = context.constructorParameter().rawType();
 		}
 		else {
 			if ( !context.constructorParameter().rawType().isAssignableFrom( Double.class ) ) {
 				throw log.invalidParameterTypeForDistanceProjectionInProjectionConstructor(
 						context.constructorParameter().rawType(), "Double" );
 			}
-			bind( context, fieldPath );
+			containerClass = null;
 		}
+		ProjectionCollector.Provider<Double, ?> collector = context.projectionCollectorProviderFactory()
+				.projectionCollectorProvider( containerClass, Double.class );
+		bind( context, fieldPath, collector );
 	}
 
-	private void bind(ProjectionBindingContext context, String fieldPath) {
+	private void bind(ProjectionBindingContext context, String fieldPath,
+			ProjectionCollector.Provider<Double, ?> collector) {
 		context.definition( Double.class, context.isIncluded( fieldPath )
-				? BeanHolder.of( new DistanceProjectionDefinition.SingleValued( fieldPath, parameterName, unit ) )
-				: ConstantProjectionDefinition.nullValue() );
-	}
-
-	private void bind(ProjectionBindingContext context, ProjectionBindingMultiContext multi, String fieldPath) {
-		multi.definition( Double.class, context.isIncluded( fieldPath )
-				? BeanHolder.of( new DistanceProjectionDefinition.MultiValued( fieldPath, parameterName, unit ) )
-				: ConstantProjectionDefinition.emptyList() );
+				? BeanHolder
+						.of( new DistanceProjectionDefinition.WrappedValued<>( fieldPath, parameterName, unit, collector ) )
+				: ConstantProjectionDefinition.empty( collector ) );
 	}
 
 	private String fieldPathOrFail(ProjectionBindingContext context) {
diff --git a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/FieldProjectionBinder.java b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/FieldProjectionBinder.java
index 49fb4c69313..18abc11d9c0 100644
--- a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/FieldProjectionBinder.java
+++ b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/FieldProjectionBinder.java
@@ -13,9 +13,9 @@
 import org.hibernate.search.engine.search.projection.definition.spi.FieldProjectionDefinition;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
 import org.hibernate.search.mapper.pojo.logging.impl.Log;
+import org.hibernate.search.mapper.pojo.model.PojoModelValue;
 import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBinder;
 import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBindingContext;
-import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBindingMultiContext;
 import org.hibernate.search.util.common.logging.impl.LoggerFactory;
 
 /**
@@ -89,29 +89,31 @@ public FieldProjectionBinder valueModel(ValueModel valueModel) {
 
 	@Override
 	public void bind(ProjectionBindingContext context) {
-		Optional<? extends ProjectionBindingMultiContext> multiOptional = context.multi();
+		Optional<PojoModelValue<?>> containerElementOptional = context.containerElement();
 		String fieldPath = fieldPathOrFail( context );
-		if ( multiOptional.isPresent() ) {
-			ProjectionBindingMultiContext multi = multiOptional.get();
-			bind( context, multi, fieldPath, multi.containerElement().rawType() );
+		Class<?> containerClass;
+		Class<?> containerElementClass;
+		if ( containerElementOptional.isPresent() ) {
+			PojoModelValue<?> containerElement = containerElementOptional.get();
+			containerElementClass = containerElement.rawType();
+			containerClass = context.constructorParameter().rawType();
 		}
 		else {
-			bind( context, fieldPath, context.constructorParameter().rawType() );
+			containerElementClass = context.constructorParameter().rawType();
+			containerClass = null;
 		}
+		bind( context, fieldPath, containerClass, containerElementClass );
 	}
 
-	private <T> void bind(ProjectionBindingContext context, String fieldPath, Class<T> constructorParameterType) {
-		context.definition( constructorParameterType, context.isIncluded( fieldPath )
-				? BeanHolder
-						.of( new FieldProjectionDefinition.SingleValued<>( fieldPath, constructorParameterType, valueModel ) )
-				: ConstantProjectionDefinition.nullValue() );
-	}
+	private <T, C> void bind(ProjectionBindingContext context, String fieldPath,
+			Class<C> containerType, Class<T> containerElementType) {
+		var collector = context.projectionCollectorProviderFactory()
+				.projectionCollectorProvider( containerType, containerElementType );
 
-	private <T> void bind(ProjectionBindingContext context, ProjectionBindingMultiContext multi, String fieldPath,
-			Class<T> containerElementType) {
-		multi.definition( containerElementType, context.isIncluded( fieldPath )
-				? BeanHolder.of( new FieldProjectionDefinition.MultiValued<>( fieldPath, containerElementType, valueModel ) )
-				: ConstantProjectionDefinition.emptyList() );
+		context.definition( containerElementType, context.isIncluded( fieldPath )
+				? BeanHolder.of( new FieldProjectionDefinition.AccumulatedValued<>( fieldPath, containerElementType,
+						collector, valueModel ) )
+				: ConstantProjectionDefinition.empty( collector ) );
 	}
 
 	private String fieldPathOrFail(ProjectionBindingContext context) {
diff --git a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/HighlightProjectionBinder.java b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/HighlightProjectionBinder.java
index b72524df6b4..b32d0a6f741 100644
--- a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/HighlightProjectionBinder.java
+++ b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/HighlightProjectionBinder.java
@@ -5,18 +5,18 @@
 package org.hibernate.search.mapper.pojo.search.definition.binding.builtin;
 
 import java.lang.invoke.MethodHandles;
-import java.util.List;
 import java.util.Optional;
 import java.util.function.Function;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.definition.ProjectionDefinitionContext;
 import org.hibernate.search.engine.search.projection.definition.spi.AbstractProjectionDefinition;
 import org.hibernate.search.engine.search.projection.dsl.SearchProjectionFactory;
 import org.hibernate.search.mapper.pojo.logging.impl.Log;
+import org.hibernate.search.mapper.pojo.model.PojoModelValue;
 import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBinder;
 import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBindingContext;
-import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBindingMultiContext;
 import org.hibernate.search.util.common.logging.impl.LoggerFactory;
 import org.hibernate.search.util.common.spi.ToStringTreeAppender;
 
@@ -83,21 +83,17 @@ public HighlightProjectionBinder highlighter(String highlighterName) {
 	@Override
 	public void bind(ProjectionBindingContext context) {
 		String fieldPath = fieldPathOrFail( context );
-		Class<?> rawType = context.constructorParameter().rawType();
-		Optional<? extends ProjectionBindingMultiContext> multiOptional = context.multi();
-
-		if ( multiOptional.isPresent() ) {
-			if ( !rawType.isAssignableFrom( List.class ) ) {
-				throw log.invalidParameterTypeForHighlightProjectionInProjectionConstructor( rawType, "List<String>" );
-			}
-			multiOptional.get().definition( String.class, new Multi( fieldPath, highlighterName ) );
-		}
-		else {
-			if ( !rawType.isAssignableFrom( String.class ) ) {
-				throw log.invalidParameterTypeForHighlightProjectionInProjectionConstructor( rawType, "String" );
-			}
-			context.definition( String.class, new Single( fieldPath, highlighterName ) );
-		}
+		Optional<PojoModelValue<?>> containerElementOptional = context.containerElement();
+
+		var collector = context.projectionCollectorProviderFactory()
+				.projectionCollectorProvider(
+						// if there's no container element, there's no container hence we are working with a "nullable" collector:
+						containerElementOptional.isPresent()
+								? context.constructorParameter().rawType()
+								: null,
+						String.class );
+
+		context.definition( String.class, new Definition<>( fieldPath, highlighterName, collector ) );
 	}
 
 	private String fieldPathOrFail(ProjectionBindingContext context) {
@@ -111,13 +107,15 @@ private String fieldPathOrFail(ProjectionBindingContext context) {
 		return paramName.get();
 	}
 
-	private abstract static class Definition<T> extends AbstractProjectionDefinition<T> {
-		protected final String fieldPath;
-		protected final String highlighterName;
+	private static class Definition<T> extends AbstractProjectionDefinition<T> {
+		private final String fieldPath;
+		private final String highlighterName;
+		private final ProjectionCollector.Provider<String, T> collector;
 
-		private Definition(String fieldPath, String highlighterName) {
+		private Definition(String fieldPath, String highlighterName, ProjectionCollector.Provider<String, T> collector) {
 			this.fieldPath = fieldPath;
 			this.highlighterName = highlighterName;
+			this.collector = collector;
 		}
 
 		@Override
@@ -125,6 +123,14 @@ protected String type() {
 			return "highlight";
 		}
 
+		@Override
+		public SearchProjection<T> create(SearchProjectionFactory<?, ?> factory, ProjectionDefinitionContext context) {
+			return factory.highlight( fieldPath )
+					.highlighter( highlighterName )
+					.collector( collector )
+					.toProjection();
+		}
+
 		@Override
 		public void appendTo(ToStringTreeAppender appender) {
 			super.appendTo( appender );
@@ -132,30 +138,4 @@ public void appendTo(ToStringTreeAppender appender) {
 			appender.attribute( "highlighter", highlighterName );
 		}
 	}
-
-	private static class Single extends Definition<String> {
-
-		private Single(String fieldPath, String highlighterName) {
-			super( fieldPath, highlighterName );
-		}
-
-		@Override
-		public SearchProjection<? extends String> create(SearchProjectionFactory<?, ?> factory,
-				ProjectionDefinitionContext context) {
-			return factory.highlight( fieldPath ).highlighter( highlighterName ).single().toProjection();
-		}
-	}
-
-	private static class Multi extends Definition<List<String>> {
-
-		private Multi(String fieldPath, String highlighterName) {
-			super( fieldPath, highlighterName );
-		}
-
-		@Override
-		public SearchProjection<List<String>> create(SearchProjectionFactory<?, ?> factory,
-				ProjectionDefinitionContext context) {
-			return factory.highlight( fieldPath ).highlighter( highlighterName ).toProjection();
-		}
-	}
 }
diff --git a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/ObjectProjectionBinder.java b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/ObjectProjectionBinder.java
index 4725753f560..139934dd3a2 100644
--- a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/ObjectProjectionBinder.java
+++ b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/builtin/ObjectProjectionBinder.java
@@ -8,11 +8,12 @@
 import java.util.Optional;
 
 import org.hibernate.search.engine.common.tree.TreeFilterDefinition;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.mapper.pojo.logging.impl.Log;
 import org.hibernate.search.mapper.pojo.mapping.definition.annotation.ObjectProjection;
+import org.hibernate.search.mapper.pojo.model.PojoModelValue;
 import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBinder;
 import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBindingContext;
-import org.hibernate.search.mapper.pojo.search.definition.binding.ProjectionBindingMultiContext;
 import org.hibernate.search.util.common.logging.impl.LoggerFactory;
 
 /**
@@ -91,26 +92,31 @@ public ObjectProjectionBinder filter(TreeFilterDefinition filter) {
 
 	@Override
 	public void bind(ProjectionBindingContext context) {
-		Optional<? extends ProjectionBindingMultiContext> multiOptional = context.multi();
+		Optional<PojoModelValue<?>> containerElementOptional = context.containerElement();
 		String fieldPath = fieldPathOrFail( context );
-		if ( multiOptional.isPresent() ) {
-			ProjectionBindingMultiContext multi = multiOptional.get();
-			bind( context, multi, fieldPath, multi.containerElement().rawType() );
+		Class<?> containerClass;
+		Class<?> containerElementClass;
+		if ( containerElementOptional.isPresent() ) {
+			PojoModelValue<?> containerElement = containerElementOptional.get();
+			containerElementClass = containerElement.rawType();
+			containerClass = context.constructorParameter().rawType();
 		}
 		else {
-			bind( context, fieldPath, context.constructorParameter().rawType() );
+			containerElementClass = context.constructorParameter().rawType();
+			containerClass = null;
 		}
+		bind( context, fieldPath, containerClass, containerElementClass );
 	}
 
-	private <T> void bind(ProjectionBindingContext context, String fieldPath, Class<T> constructorParameterType) {
-		context.definition( constructorParameterType,
-				context.createObjectDefinition( fieldPath, constructorParameterType, filter ) );
-	}
+	private <T, C> void bind(ProjectionBindingContext context, String fieldPath, Class<C> containerType,
+			Class<T> containerElementType) {
+		ProjectionCollector.Provider<T, ?> collector = context.projectionCollectorProviderFactory()
+				.projectionCollectorProvider( containerType, containerElementType );
 
-	private <T> void bind(ProjectionBindingContext context, ProjectionBindingMultiContext multi,
-			String fieldPath, Class<T> containerElementType) {
-		multi.definition( containerElementType,
-				context.createObjectDefinitionMulti( fieldPath, containerElementType, filter ) );
+		context.definition(
+				containerElementType,
+				context.createObjectDefinition( fieldPath, containerElementType, filter, collector )
+		);
 	}
 
 	private String fieldPathOrFail(ProjectionBindingContext context) {
diff --git a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/impl/ProjectionBindingContextImpl.java b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/impl/ProjectionBindingContextImpl.java
index 9a969fc3590..f31414446c3 100644
--- a/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/impl/ProjectionBindingContextImpl.java
+++ b/mapper/pojo-base/src/main/java/org/hibernate/search/mapper/pojo/search/definition/binding/impl/ProjectionBindingContextImpl.java
@@ -5,9 +5,12 @@
 package org.hibernate.search.mapper.pojo.search.definition.binding.impl;
 
 import java.lang.invoke.MethodHandles;
+import java.util.Collection;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
+import java.util.Set;
+import java.util.SortedSet;
 import java.util.function.BiFunction;
 import java.util.function.Function;
 
@@ -17,6 +20,8 @@
 import org.hibernate.search.engine.environment.bean.BeanHolder;
 import org.hibernate.search.engine.environment.bean.BeanResolver;
 import org.hibernate.search.engine.mapper.model.spi.MappingElement;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
+import org.hibernate.search.engine.search.projection.ProjectionCollectorProviderFactory;
 import org.hibernate.search.engine.search.projection.definition.ProjectionDefinition;
 import org.hibernate.search.engine.search.projection.definition.spi.CompositeProjectionDefinition;
 import org.hibernate.search.engine.search.projection.definition.spi.ConstantProjectionDefinition;
@@ -51,22 +56,48 @@ public class ProjectionBindingContextImpl<P> implements ProjectionBindingContext
 			(mappingElement, cyclicRecursionPath) -> log.objectProjectionCyclicRecursion( mappingElement,
 					mappingElement.eventContext(), cyclicRecursionPath );
 
+	private static final Set<String> CONTAINER_EXTRACTORS = Set.of(
+			BuiltinContainerExtractors.ARRAY_OBJECT,
+			BuiltinContainerExtractors.ARRAY_CHAR,
+			BuiltinContainerExtractors.ARRAY_BOOLEAN,
+			BuiltinContainerExtractors.ARRAY_BYTE,
+			BuiltinContainerExtractors.ARRAY_SHORT,
+			BuiltinContainerExtractors.ARRAY_INT,
+			BuiltinContainerExtractors.ARRAY_LONG,
+			BuiltinContainerExtractors.ARRAY_FLOAT,
+			BuiltinContainerExtractors.ARRAY_DOUBLE,
+			BuiltinContainerExtractors.COLLECTION,
+			BuiltinContainerExtractors.ITERABLE,
+			// and some single ones:
+			BuiltinContainerExtractors.OPTIONAL,
+			BuiltinContainerExtractors.OPTIONAL_DOUBLE,
+			BuiltinContainerExtractors.OPTIONAL_INT,
+			BuiltinContainerExtractors.OPTIONAL_LONG
+	);
+
+	private static final Set<String> MULTI_EXTRACTORS = Set.of(
+			BuiltinContainerExtractors.COLLECTION,
+			BuiltinContainerExtractors.ITERABLE
+	);
+
 	private final PojoMappingHelper mappingHelper;
 	final ProjectionConstructorParameterBinder<P> parameterBinder;
 	private final Map<String, Object> params;
 	private final PojoTypeModel<?> parameterTypeModel;
 	private final PojoModelConstructorParameterRootElement<P> parameterRootElement;
+	private final ProjectionCollectorProviderFactory projectionCollectorProviderFactory;
 
 	private MappingElement mappingElement;
 	private PartialBinding<P> partialBinding;
 
-	public ProjectionBindingContextImpl(ProjectionConstructorParameterBinder<P> parameterBinder,
+	ProjectionBindingContextImpl(ProjectionConstructorParameterBinder<P> parameterBinder,
 			Map<String, Object> params) {
 		this.mappingHelper = parameterBinder.mappingHelper;
 		this.parameterBinder = parameterBinder;
 		this.params = params;
 		this.parameterTypeModel = parameterBinder.parameter.typeModel();
 		this.parameterRootElement = parameterBinder.parameterRootElement;
+		this.projectionCollectorProviderFactory = new BuiltInProjectionCollectorProviderFactory();
 	}
 
 	@Override
@@ -96,34 +127,46 @@ public <T> Optional<T> paramOptional(String name, Class<T> paramType) {
 	}
 
 	@Override
-	public <P2> void definition(Class<P2> expectedValueType, ProjectionDefinition<? extends P2> definition) {
+	public <P2, C> void definition(Class<P2> expectedValueType, ProjectionDefinition<? extends C> definition) {
 		definition( expectedValueType, BeanHolder.of( definition ) );
 	}
 
 	@Override
-	public <P2> void definition(Class<P2> expectedValueType,
-			BeanHolder<? extends ProjectionDefinition<? extends P2>> definitionHolder) {
+	public <P2, C> void definition(Class<P2> expectedValueType,
+			BeanHolder<? extends ProjectionDefinition<? extends C>> definitionHolder) {
 		checkAndBind( definitionHolder, mappingHelper.introspector().typeModel( expectedValueType ) );
 	}
 
+	@SuppressWarnings("deprecation")
 	@Override
 	public Optional<MultiContextImpl<?>> multi() {
+		PojoTypeModel<?> boundParameterElement = boundParameterElement( MULTI_EXTRACTORS );
+		if ( boundParameterElement == null ) {
+			return Optional.empty();
+		}
+		else {
+			if ( !mappingHelper.introspector().typeModel( List.class ).isSubTypeOf( parameterTypeModel.rawType() ) ) {
+				throw log.invalidMultiValuedParameterTypeForProjectionConstructor( parameterTypeModel );
+			}
+			return Optional.of( new MultiContextImpl<>( boundParameterElement ) );
+		}
+	}
+
+	private PojoTypeModel<?> boundParameterElement(Set<String> extractors) {
 		BoundContainerExtractorPath<?, ?> boundParameterElementPath = mappingHelper.indexModelBinder()
 				.bindExtractorPath( parameterTypeModel, ContainerExtractorPath.defaultExtractors() );
 		List<String> boundParameterElementExtractorNames =
 				boundParameterElementPath.getExtractorPath().explicitExtractorNames();
 
 		if ( boundParameterElementExtractorNames.isEmpty() ) {
-			return Optional.empty();
+			return null;
 		}
 		else {
 			if ( boundParameterElementExtractorNames.size() > 1
-					|| !( BuiltinContainerExtractors.COLLECTION.equals( boundParameterElementExtractorNames.get( 0 ) )
-							|| BuiltinContainerExtractors.ITERABLE.equals( boundParameterElementExtractorNames.get( 0 ) ) )
-					|| !mappingHelper.introspector().typeModel( List.class ).isSubTypeOf( parameterTypeModel.rawType() ) ) {
+					|| !( extractors.contains( boundParameterElementExtractorNames.get( 0 ) ) ) ) {
 				throw log.invalidMultiValuedParameterTypeForProjectionConstructor( parameterTypeModel );
 			}
-			return Optional.of( new MultiContextImpl<>( boundParameterElementPath.getExtractedType() ) );
+			return boundParameterElementPath.getExtractedType();
 		}
 	}
 
@@ -133,53 +176,48 @@ public PojoModelConstructorParameter constructorParameter() {
 	}
 
 	@Override
-	public <T> BeanHolder<? extends ProjectionDefinition<T>> createObjectDefinition(String fieldPath,
-			Class<T> projectedType, TreeFilterDefinition filter) {
-		Contracts.assertNotNull( fieldPath, "fieldPath" );
-		Contracts.assertNotNull( projectedType, "projectedType" );
-		Contracts.assertNotNull( filter, "filter" );
-		Optional<BeanHolder<? extends ProjectionDefinition<T>>> objectProjection = nestObjectProjection(
-				fieldPath, filter,
-				nestingContext -> {
-					CompositeProjectionDefinition<T> composite =
-							createCompositeProjectionDefinition( projectedType, nestingContext );
-					try {
-						return BeanHolder.ofCloseable( new ObjectProjectionDefinition.SingleValued<>(
-								fieldPath, composite ) );
-					}
-					catch (RuntimeException e) {
-						new SuppressingCloser( e )
-								.push( composite );
-						throw e;
-					}
-				}
-		);
-		return objectProjection.orElse( ConstantProjectionDefinition.nullValue() );
+	public Optional<PojoModelValue<?>> containerElement() {
+		return containerElementModel().map( this::getPojoModelValueElement );
+	}
+
+	private PojoModelValueElement<?> getPojoModelValueElement(PojoTypeModel<?> m) {
+		return new PojoModelValueElement<>( mappingHelper.introspector(), m );
+	}
+
+	private Optional<PojoTypeModel<?>> containerElementModel() {
+		PojoTypeModel<?> boundParameterElement = boundParameterElement( CONTAINER_EXTRACTORS );
+		if ( boundParameterElement == null ) {
+			return Optional.empty();
+		}
+		else {
+			return Optional.of( boundParameterElement );
+		}
 	}
 
 	@Override
-	public <T> BeanHolder<? extends ProjectionDefinition<List<T>>> createObjectDefinitionMulti(String fieldPath,
-			Class<T> projectedType, TreeFilterDefinition filter) {
+	public <C, T> BeanHolder<? extends ProjectionDefinition<C>> createObjectDefinition(String fieldPath,
+			Class<T> projectedType, TreeFilterDefinition filter,
+			ProjectionCollector.Provider<T, C> collector) {
 		Contracts.assertNotNull( fieldPath, "fieldPath" );
 		Contracts.assertNotNull( projectedType, "projectedType" );
 		Contracts.assertNotNull( filter, "filter" );
-		Optional<BeanHolder<? extends ProjectionDefinition<List<T>>>> objectProjection = nestObjectProjection(
+		Contracts.assertNotNull( collector, "collector" );
+		Optional<BeanHolder<? extends ProjectionDefinition<C>>> objectProjection = nestObjectProjection(
 				fieldPath, filter,
 				nestingContext -> {
 					CompositeProjectionDefinition<T> composite =
 							createCompositeProjectionDefinition( projectedType, nestingContext );
 					try {
-						return BeanHolder.ofCloseable( new ObjectProjectionDefinition.MultiValued<>(
-								fieldPath, composite ) );
+						return BeanHolder.ofCloseable( new ObjectProjectionDefinition.WrappedValued<>(
+								fieldPath, composite, collector ) );
 					}
 					catch (RuntimeException e) {
-						new SuppressingCloser( e )
-								.push( composite );
+						new SuppressingCloser( e ).push( composite );
 						throw e;
 					}
 				}
 		);
-		return objectProjection.orElse( ConstantProjectionDefinition.emptyList() );
+		return objectProjection.orElse( ConstantProjectionDefinition.empty( collector ) );
 	}
 
 	private <T> Optional<T> nestObjectProjection(String fieldPath, TreeFilterDefinition filter,
@@ -232,6 +270,11 @@ public boolean isIncluded(String fieldPath) {
 				(prefixedRelativeName, inclusion) -> TreeNodeInclusion.INCLUDED.equals( inclusion ) );
 	}
 
+	@Override
+	public ProjectionCollectorProviderFactory projectionCollectorProviderFactory() {
+		return projectionCollectorProviderFactory;
+	}
+
 	public BeanHolder<? extends ProjectionDefinition<? extends P>> applyBinder(ProjectionBinder binder) {
 		try {
 			this.mappingElement = new PojoConstructorParameterProjectionMappingElement( parameterBinder.parent.constructor,
@@ -256,9 +299,17 @@ public BeanHolder<? extends ProjectionDefinition<? extends P>> applyBinder(Proje
 		}
 	}
 
-	private <P2> void checkAndBind(BeanHolder<? extends ProjectionDefinition<? extends P2>> definitionHolder,
+	private <P2, C> void checkAndBind(BeanHolder<? extends ProjectionDefinition<? extends C>> definitionHolder,
 			PojoRawTypeModel<P2> expectedValueType) {
-		if ( !expectedValueType.isSubTypeOf( parameterTypeModel.rawType() ) ) {
+		Optional<PojoTypeModel<?>> containerElementModel = containerElementModel();
+		if ( containerElementModel.isPresent() ) {
+			if ( !expectedValueType.isSubTypeOf( containerElementModel.get().rawType() ) ) {
+				throw log.invalidOutputTypeForMultiValuedProjectionDefinition( definitionHolder.get(), parameterTypeModel,
+						expectedValueType
+				);
+			}
+		}
+		else if ( !expectedValueType.isSubTypeOf( parameterTypeModel.rawType() ) ) {
 			throw log.invalidOutputTypeForProjectionDefinition( definitionHolder.get(), parameterTypeModel, expectedValueType );
 		}
 
@@ -270,15 +321,13 @@ private <P2> void checkAndBind(BeanHolder<? extends ProjectionDefinition<? exten
 	}
 
 	public BeanHolder<? extends ProjectionDefinition<?>> applyDefaultProjection() {
-		Optional<? extends ProjectionBindingContextImpl<?>.MultiContextImpl<?>> multi = multi();
+		Optional<PojoTypeModel<?>> containerElement = containerElementModel();
 		PojoConstructorModel<?> constructorModelOrNull;
-		if ( multi.isPresent() ) {
-			constructorModelOrNull = parameterBinder.findProjectionConstructorOrNull(
-					multi.get().parameterContainerElementTypeModel.rawType() );
+		if ( containerElement.isPresent() ) {
+			constructorModelOrNull = parameterBinder.findProjectionConstructorOrNull( containerElement.get().rawType() );
 		}
 		else {
-			constructorModelOrNull = parameterBinder.findProjectionConstructorOrNull(
-					parameterTypeModel.rawType() );
+			constructorModelOrNull = parameterBinder.findProjectionConstructorOrNull( parameterTypeModel.rawType() );
 		}
 		Optional<String> paramName = parameterRootElement.name();
 		if ( !paramName.isPresent() ) {
@@ -310,6 +359,7 @@ BeanHolder<? extends ProjectionDefinition<? extends P>> complete() {
 		}
 	}
 
+	@Deprecated(since = "8.0")
 	public class MultiContextImpl<PV> implements ProjectionBindingMultiContext {
 		public final PojoTypeModel<PV> parameterContainerElementTypeModel;
 		private final PojoModelValue<PV> parameterContainerElementRootElement;
@@ -333,23 +383,48 @@ public <P2> void definition(Class<P2> expectedValueType,
 		}
 
 		@Override
-		public PojoModelValue<?> containerElement() {
+		public PojoModelValue<PV> containerElement() {
 			return parameterContainerElementRootElement;
 		}
 
-		private <P2> void checkAndBind(
-				BeanHolder<? extends ProjectionDefinition<? extends List<? extends P2>>> definitionHolder,
-				PojoRawTypeModel<P2> expectedValueType) {
-			if ( !expectedValueType.isSubTypeOf( parameterContainerElementTypeModel.rawType() ) ) {
-				throw log.invalidOutputTypeForMultiValuedProjectionDefinition( definitionHolder.get(), parameterTypeModel,
-						expectedValueType );
-			}
+	}
 
-			@SuppressWarnings("unchecked") // We check that P2 extends PV explicitly using reflection (see above) and we've already checked that P = List<? extends PV>
-			BeanHolder<? extends ProjectionDefinition<? extends P>> castDefinitionHolder =
-					(BeanHolder<? extends ProjectionDefinition<? extends P>>) definitionHolder;
+	private class BuiltInProjectionCollectorProviderFactory implements ProjectionCollectorProviderFactory {
+
+		@SuppressWarnings({ "rawtypes", "unchecked" })
+		@Override
+		public <R, U> ProjectionCollector.Provider<U, R> projectionCollectorProvider(Class<R> containerType,
+				Class<U> containerElementType) {
+			ProjectionCollector.Provider reference;
+			if ( containerType == null ) {
+				reference = ProjectionCollector.nullable();
+			}
+			else if ( List.class.isAssignableFrom( containerType ) ) {
+				reference = ProjectionCollector.list();
+			}
+			else if ( SortedSet.class.isAssignableFrom( containerType ) ) {
+				if ( !Comparable.class.isAssignableFrom( containerElementType ) ) {
+					throw log.cannotBindSortedSetWithNonComparableElements(
+							containerElementType,
+							mappingElement.eventContext()
+					);
+				}
+				reference = ProjectionCollector.sortedSet();
+			}
+			else if ( Set.class.isAssignableFrom( containerType ) ) {
+				reference = ProjectionCollector.set();
+			}
+			else if ( containerType.isArray() ) {
+				reference = ProjectionCollector.array( containerElementType );
+			}
+			else if ( Collection.class.isAssignableFrom( containerType ) || Iterable.class.isAssignableFrom( containerType ) ) {
+				reference = ProjectionCollector.list();
+			}
+			else {
+				throw log.invalidMultiValuedParameterTypeForProjectionConstructor( parameterTypeModel );
+			}
 
-			partialBinding = new PartialBinding<>( castDefinitionHolder );
+			return reference;
 		}
 	}
 }
diff --git a/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/assertion/TestComparators.java b/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/assertion/TestComparators.java
index 71c7fbb1dd0..bdf3d010a82 100644
--- a/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/assertion/TestComparators.java
+++ b/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/assertion/TestComparators.java
@@ -6,6 +6,7 @@
 
 import java.util.Comparator;
 import java.util.Iterator;
+import java.util.Optional;
 
 public class TestComparators {
 
@@ -60,4 +61,40 @@ else if ( bIt.hasNext() ) {
 			}
 		} );
 	}
+
+	public static <T> Comparator<Optional<T>> optional(Comparator<T> elementComparator) {
+		return Comparator.nullsFirst( (a, b) -> {
+			if ( a.isPresent() && b.isPresent() ) {
+				return elementComparator.compare( a.get(), b.get() );
+			}
+			if ( a.isEmpty() && b.isEmpty() ) {
+				return 0;
+			}
+			return a.isEmpty() ? -1 : 1;
+		} );
+	}
+
+	public static <T> Comparator<T[]> array(Comparator<T> elementComparator) {
+		return Comparator.nullsFirst( (a, b) -> {
+			int index = 0;
+			int min = Math.min( a.length, b.length );
+			for ( ; index < min; index++ ) {
+				T aElem = a[index];
+				T bElem = b[index];
+				int elemOrder = elementComparator.compare( aElem, bElem );
+				if ( elemOrder != 0 ) {
+					return elemOrder; // lexicographical ordering: the first differing element dictates the order.
+				}
+			}
+			if ( a.length < b.length ) {
+				return -1; // b is a prefix of a
+			}
+			else if ( a.length > b.length ) {
+				return 1; // a is a prefix of b
+			}
+			else {
+				return 0; // a and b have the same number of elements, all equal according to the element comparator
+			}
+		} );
+	}
 }
diff --git a/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubCompositeProjection.java b/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubCompositeProjection.java
index edcc6267744..eb270e2921b 100644
--- a/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubCompositeProjection.java
+++ b/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubCompositeProjection.java
@@ -7,51 +7,50 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.Iterator;
-import java.util.List;
 
 import org.hibernate.search.engine.search.loading.spi.LoadingResult;
 import org.hibernate.search.engine.search.loading.spi.ProjectionHitMapper;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.spi.CompositeProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionCompositor;
 
 class StubCompositeProjection<E, V, A, P> extends StubSearchProjection<P> {
 
 	private final StubSearchProjection<?>[] inners;
 	private final ProjectionCompositor<E, V> compositor;
-	private final ProjectionAccumulator<E, V, A, P> accumulator;
+	private final ProjectionCollector<E, V, A, P> collector;
 	private final boolean singleValued;
 
 	protected StubCompositeProjection(StubSearchProjection<?>[] inners, ProjectionCompositor<E, V> compositor,
-			ProjectionAccumulator<E, V, A, P> accumulator, boolean singleValued) {
+			ProjectionCollector<E, V, A, P> collector, boolean singleValued) {
 		this.inners = inners;
 		this.compositor = compositor;
-		this.accumulator = accumulator;
+		this.collector = collector;
 		this.singleValued = singleValued;
 	}
 
 	@Override
 	public Object extract(ProjectionHitMapper<?> projectionHitMapper, Iterator<?> projectionFromIndex,
 			StubSearchProjectionContext context) {
-		List<?> allInnerProjectionsFromIndex;
+		Iterable<?> allInnerProjectionsFromIndex;
 		if ( singleValued ) {
 			Object singleValue = projectionFromIndex.next();
 			allInnerProjectionsFromIndex = singleValue == null ? Collections.emptyList() : Arrays.asList( singleValue );
 		}
 		else {
-			allInnerProjectionsFromIndex = (List<?>) projectionFromIndex.next();
+			allInnerProjectionsFromIndex = (Iterable<?>) projectionFromIndex.next();
 		}
 
-		A accumulated = accumulator.createInitial();
+		A accumulated = collector.createInitial();
 		for ( Object innerProjectionsFromIndex : allInnerProjectionsFromIndex ) {
 			E extractedData = compositor.createInitial();
-			Iterator<?> innerProjectionFromIndex = ( (List<?>) innerProjectionsFromIndex ).iterator();
+			Iterator<?> innerProjectionFromIndex = ( (Iterable<?>) innerProjectionsFromIndex ).iterator();
 			for ( int i = 0; i < inners.length; i++ ) {
 				Object extractedDataForInner = inners[i].extract( projectionHitMapper, innerProjectionFromIndex, context );
 				extractedData = compositor.set( extractedData, i, extractedDataForInner );
 			}
-			accumulated = accumulator.accumulate( accumulated, extractedData );
+			accumulated = collector.accumulate( accumulated, extractedData );
 		}
 		return accumulated;
 	}
@@ -60,17 +59,17 @@ public Object extract(ProjectionHitMapper<?> projectionHitMapper, Iterator<?> pr
 	@SuppressWarnings("unchecked")
 	public P transform(LoadingResult<?> loadingResult, Object extractedData, StubSearchProjectionContext context) {
 		A accumulated = (A) extractedData;
-		for ( int i = 0; i < accumulator.size( accumulated ); i++ ) {
-			E transformedData = accumulator.get( accumulated, i );
+		for ( int i = 0; i < collector.size( accumulated ); i++ ) {
+			E transformedData = collector.get( accumulated, i );
 			// Transform in-place
 			for ( int j = 0; j < inners.length; j++ ) {
 				Object extractedDataForInner = compositor.get( transformedData, j );
 				Object transformedDataForInner = inners[j].transform( loadingResult, extractedDataForInner, context );
 				transformedData = compositor.set( transformedData, j, transformedDataForInner );
 			}
-			accumulated = accumulator.transform( accumulated, i, compositor.finish( transformedData ) );
+			accumulated = collector.transform( accumulated, i, compositor.finish( transformedData ) );
 		}
-		return accumulator.finish( accumulated );
+		return collector.finish( accumulated );
 	}
 
 	@Override
@@ -82,7 +81,7 @@ protected String typeName() {
 	protected void toNode(StubProjectionNode.Builder self) {
 		// Not including the compositor to facilitate assertions
 		// self.attribute( "compositor", compositor );
-		self.attribute( "accumulator", accumulator );
+		self.attribute( "collector", collector );
 		self.attribute( "singleValued", singleValued );
 		for ( StubSearchProjection<?> inner : inners ) {
 			appendInnerNode( self, "inner", inner );
@@ -96,19 +95,19 @@ static class Builder implements CompositeProjectionBuilder {
 
 		@Override
 		public final <E, V, P> SearchProjection<P> build(SearchProjection<?>[] inners, ProjectionCompositor<E, V> compositor,
-				ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
+				ProjectionCollector.Provider<V, P> collectorProvider) {
 			StubSearchProjection<?>[] typedInners =
 					new StubSearchProjection<?>[inners.length];
 			for ( int i = 0; i < inners.length; i++ ) {
 				typedInners[i] = StubSearchProjection.from( inners[i] );
 			}
-			return doBuild( typedInners, compositor, accumulatorProvider.get(), accumulatorProvider.isSingleValued() );
+			return doBuild( typedInners, compositor, collectorProvider.get(), collectorProvider.isSingleValued() );
 		}
 
 		protected <E, V, A, P> SearchProjection<P> doBuild(StubSearchProjection<?>[] typedInners,
 				ProjectionCompositor<E, V> compositor,
-				ProjectionAccumulator<E, V, A, P> accumulator, boolean singleValued) {
-			return new StubCompositeProjection<>( typedInners, compositor, accumulator, singleValued );
+				ProjectionCollector<E, V, A, P> collector, boolean singleValued) {
+			return new StubCompositeProjection<>( typedInners, compositor, collector, singleValued );
 		}
 	}
 }
diff --git a/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubDistanceToFieldProjection.java b/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubDistanceToFieldProjection.java
index c49279144cc..82707d8ab37 100644
--- a/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubDistanceToFieldProjection.java
+++ b/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubDistanceToFieldProjection.java
@@ -4,9 +4,9 @@
  */
 package org.hibernate.search.util.impl.integrationtest.common.stub.backend.search.projection.impl;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.spi.DistanceToFieldProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.spatial.DistanceUnit;
 import org.hibernate.search.engine.spatial.GeoPoint;
 import org.hibernate.search.util.common.AssertionFailure;
@@ -39,7 +39,7 @@ public void unit(DistanceUnit unit) {
 		}
 
 		@Override
-		public <P> SearchProjection<P> build(ProjectionAccumulator.Provider<Double, P> accumulatorProvider) {
+		public <P> SearchProjection<P> build(ProjectionCollector.Provider<Double, P> collectorProvider) {
 			throw new AssertionFailure( "Distance projections are not supported in the stub backend." );
 		}
 	}
diff --git a/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubFieldHighlightProjection.java b/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubFieldHighlightProjection.java
index b3cb8fac466..ea1df494f89 100644
--- a/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubFieldHighlightProjection.java
+++ b/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubFieldHighlightProjection.java
@@ -8,20 +8,23 @@
 
 import org.hibernate.search.engine.search.loading.spi.LoadingResult;
 import org.hibernate.search.engine.search.loading.spi.ProjectionHitMapper;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.dsl.spi.HighlightProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.util.impl.integrationtest.common.stub.backend.search.common.impl.AbstractStubSearchQueryElementFactory;
 import org.hibernate.search.util.impl.integrationtest.common.stub.backend.search.common.impl.StubSearchIndexNodeContext;
 import org.hibernate.search.util.impl.integrationtest.common.stub.backend.search.common.impl.StubSearchIndexScope;
 
-public class StubFieldHighlightProjection<T> extends StubSearchProjection<T> {
+public class StubFieldHighlightProjection<T, A> extends StubSearchProjection<T> {
 	private final String fieldPath;
 	private final String highlighterName;
+	private final ProjectionCollector<Object, String, A, T> collector;
 
-	public StubFieldHighlightProjection(String fieldPath, String highlighterName) {
+	public StubFieldHighlightProjection(String fieldPath, String highlighterName,
+			ProjectionCollector<Object, String, A, T> collector) {
 		this.fieldPath = fieldPath;
 		this.highlighterName = highlighterName;
+		this.collector = collector;
 	}
 
 	@Override
@@ -32,9 +35,8 @@ public Object extract(ProjectionHitMapper<?> projectionHitMapper, Iterator<?> pr
 
 	@Override
 	@SuppressWarnings("unchecked")
-	public T transform(LoadingResult<?> loadingResult, Object extractedData,
-			StubSearchProjectionContext context) {
-		return (T) extractedData;
+	public T transform(LoadingResult<?> loadingResult, Object extractedData, StubSearchProjectionContext context) {
+		return collector.finish( (A) extractedData );
 	}
 
 	@Override
@@ -62,8 +64,8 @@ static class Builder extends HighlightProjectionBuilder {
 		}
 
 		@Override
-		public <V> SearchProjection<V> build(ProjectionAccumulator.Provider<String, V> accumulatorProvider) {
-			return new StubFieldHighlightProjection<>( path, highlighterName );
+		public <V> SearchProjection<V> build(ProjectionCollector.Provider<String, V> collectorProvider) {
+			return new StubFieldHighlightProjection<>( path, highlighterName, collectorProvider.get() );
 		}
 	}
 }
diff --git a/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubFieldProjection.java b/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubFieldProjection.java
index f2916f756f0..21688cebcaf 100644
--- a/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubFieldProjection.java
+++ b/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubFieldProjection.java
@@ -7,15 +7,14 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.Iterator;
-import java.util.List;
 
 import org.hibernate.search.engine.backend.types.converter.spi.ProjectionConverter;
 import org.hibernate.search.engine.search.common.ValueModel;
 import org.hibernate.search.engine.search.loading.spi.LoadingResult;
 import org.hibernate.search.engine.search.loading.spi.ProjectionHitMapper;
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.spi.FieldProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.util.impl.integrationtest.common.stub.backend.search.common.impl.AbstractStubSearchQueryElementFactory;
 import org.hibernate.search.util.impl.integrationtest.common.stub.backend.search.common.impl.StubSearchIndexNodeContext;
 import org.hibernate.search.util.impl.integrationtest.common.stub.backend.search.common.impl.StubSearchIndexScope;
@@ -26,34 +25,34 @@ public class StubFieldProjection<F, V, A, P> extends StubSearchProjection<P> {
 	private final Class<F> fieldType;
 	private final Class<V> expectedType;
 	private final ProjectionConverter<F, ? extends V> converter;
-	private final ProjectionAccumulator<F, V, A, P> accumulator;
+	private final ProjectionCollector<F, V, A, P> collector;
 	private final boolean singleValued;
 
 	public StubFieldProjection(String fieldPath, Class<F> fieldType, Class<V> expectedType,
 			ProjectionConverter<F, ? extends V> converter,
-			ProjectionAccumulator<F, V, A, P> accumulator, boolean singleValued) {
+			ProjectionCollector<F, V, A, P> collector, boolean singleValued) {
 		this.fieldPath = fieldPath;
 		this.fieldType = fieldType;
 		this.expectedType = expectedType;
 		this.converter = converter;
-		this.accumulator = accumulator;
+		this.collector = collector;
 		this.singleValued = singleValued;
 	}
 
 	@Override
 	public A extract(ProjectionHitMapper<?> projectionHitMapper, Iterator<?> projectionFromIndex,
 			StubSearchProjectionContext context) {
-		List<?> fieldValues;
+		Iterable<?> fieldValues;
 		if ( singleValued ) {
 			Object singleValue = projectionFromIndex.next();
 			fieldValues = singleValue == null ? Collections.emptyList() : Arrays.asList( singleValue );
 		}
 		else {
-			fieldValues = (List<?>) projectionFromIndex.next();
+			fieldValues = (Iterable<?>) projectionFromIndex.next();
 		}
-		A accumulated = accumulator.createInitial();
+		A accumulated = collector.createInitial();
 		for ( Object fieldValue : fieldValues ) {
-			accumulated = accumulator.accumulate( accumulated, fieldType.cast( fieldValue ) );
+			accumulated = collector.accumulate( accumulated, fieldType.cast( fieldValue ) );
 		}
 		return accumulated;
 	}
@@ -63,8 +62,9 @@ public A extract(ProjectionHitMapper<?> projectionHitMapper, Iterator<?> project
 	public P transform(LoadingResult<?> loadingResult, Object extractedData,
 			StubSearchProjectionContext context) {
 		A accumulated = (A) extractedData;
-		A transformedData = accumulator.transformAll( accumulated, converter, context.fromDocumentValueConvertContext() );
-		return accumulator.finish( transformedData );
+		A transformedData = collector.transformAll( accumulated, converter.delegate(),
+				context.fromDocumentValueConvertContext() );
+		return collector.finish( transformedData );
 	}
 
 	@Override
@@ -78,7 +78,7 @@ protected void toNode(StubProjectionNode.Builder self) {
 		self.attribute( "fieldType", fieldType );
 		self.attribute( "expectedType", expectedType );
 		self.attribute( "converter", converter );
-		self.attribute( "accumulator", accumulator );
+		self.attribute( "collector", collector );
 		self.attribute( "singleValued", singleValued );
 	}
 
@@ -120,9 +120,9 @@ static class Builder<F, V> implements FieldProjectionBuilder<V> {
 		}
 
 		@Override
-		public <P> SearchProjection<P> build(ProjectionAccumulator.Provider<V, P> accumulatorProvider) {
+		public <P> SearchProjection<P> build(ProjectionCollector.Provider<V, P> collectorProvider) {
 			return new StubFieldProjection<>( fieldPath, valueClass, expectedType, converter,
-					accumulatorProvider.get(), accumulatorProvider.isSingleValued() );
+					collectorProvider.get(), collectorProvider.isSingleValued() );
 		}
 	}
 }
diff --git a/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubObjectProjection.java b/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubObjectProjection.java
index 029d4a49d04..b8e6214b032 100644
--- a/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubObjectProjection.java
+++ b/util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/stub/backend/search/projection/impl/StubObjectProjection.java
@@ -4,9 +4,9 @@
  */
 package org.hibernate.search.util.impl.integrationtest.common.stub.backend.search.projection.impl;
 
+import org.hibernate.search.engine.search.projection.ProjectionCollector;
 import org.hibernate.search.engine.search.projection.SearchProjection;
 import org.hibernate.search.engine.search.projection.spi.CompositeProjectionBuilder;
-import org.hibernate.search.engine.search.projection.spi.ProjectionAccumulator;
 import org.hibernate.search.engine.search.projection.spi.ProjectionCompositor;
 import org.hibernate.search.util.impl.integrationtest.common.stub.backend.search.common.impl.AbstractStubSearchQueryElementFactory;
 import org.hibernate.search.util.impl.integrationtest.common.stub.backend.search.common.impl.StubSearchIndexNodeContext;
@@ -17,9 +17,9 @@ public class StubObjectProjection<E, V, A, P> extends StubCompositeProjection<E,
 	private final String objectFieldPath;
 
 	private StubObjectProjection(String objectFieldPath, StubSearchProjection<?>[] inners,
-			ProjectionCompositor<E, V> compositor, ProjectionAccumulator<E, V, A, P> accumulator,
+			ProjectionCompositor<E, V> compositor, ProjectionCollector<E, V, A, P> collector,
 			boolean singleValued) {
-		super( inners, compositor, accumulator, singleValued );
+		super( inners, compositor, collector, singleValued );
 		this.objectFieldPath = objectFieldPath;
 	}
 
@@ -51,9 +51,9 @@ static class Builder extends StubCompositeProjection.Builder {
 
 		@Override
 		protected <E, V, A, P> SearchProjection<P> doBuild(StubSearchProjection<?>[] typedInners,
-				ProjectionCompositor<E, V> compositor, ProjectionAccumulator<E, V, A, P> accumulator,
+				ProjectionCompositor<E, V> compositor, ProjectionCollector<E, V, A, P> collector,
 				boolean singleValued) {
-			return new StubObjectProjection<>( objectFieldPath, typedInners, compositor, accumulator, singleValued );
+			return new StubObjectProjection<>( objectFieldPath, typedInners, compositor, collector, singleValued );
 		}
 	}
 }