diff --git a/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/cst/path/RootSlashPath.java b/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/cst/path/RootSlashPath.java
index 1be0d9bf6..4d0cec884 100644
--- a/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/cst/path/RootSlashPath.java
+++ b/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/cst/path/RootSlashPath.java
@@ -61,7 +61,8 @@ public ISequence<?> accept(
 
     ISequence<?> roots = ObjectUtils.notNull(focus.stream()
         .map(ItemUtils::checkItemIsNodeItemForStep)
-        .map(item -> Axis.ANCESTOR_OR_SELF.execute(ObjectUtils.notNull(item)).findFirst().get())
+        // the previous checks for a null instance
+        .flatMap(item -> Axis.ANCESTOR_OR_SELF.execute(ObjectUtils.notNull(item)).limit(1))
         .collect(ISequence.toSequence()));
 
     return getExpression().accept(dynamicContext, roots);
diff --git a/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/IFunction.java b/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/IFunction.java
index 35ba12bdb..224fce0f5 100644
--- a/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/IFunction.java
+++ b/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/IFunction.java
@@ -228,28 +228,13 @@ ISequence<?> execute(
    */
   @NonNull
   default String toSignature() {
-    StringBuilder builder = new StringBuilder()
-        .append("Q{")
-        .append(getNamespace())
-        .append('}')
-        .append(getName()) // name
-        .append('('); // arguments
-
-    List<IArgument> arguments = getArguments();
-    if (arguments.isEmpty()) {
-      builder.append("()");
-    } else {
-      builder.append(arguments.stream().map(IArgument::toSignature).collect(Collectors.joining(",")));
-
-      if (isArityUnbounded()) {
-        builder.append(", ...");
-      }
-    }
-
-    builder.append(") as ")
-        .append(getResult().toSignature());// return type
-
-    return ObjectUtils.notNull(builder.toString());
+    return ObjectUtils.notNull(String.format("Q{%s}%s(%s) as %s",
+        getNamespace(),
+        getName(),
+        getArguments().isEmpty() ? "()"
+            : getArguments().stream().map(IArgument::toSignature).collect(Collectors.joining(","))
+                + (isArityUnbounded() ? ", ..." : ""),
+        getResult().toSignature()));
   }
 
   /**
diff --git a/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnDocumentUri.java b/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnDocumentUri.java
index 1bb8c0c7e..64c8f602f 100644
--- a/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnDocumentUri.java
+++ b/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnDocumentUri.java
@@ -88,14 +88,9 @@ private static ISequence<IAnyUriItem> executeNoArg(@NonNull IFunction function,
 
     INodeItem item = FunctionUtils.requireTypeOrNull(INodeItem.class, focus);
 
-    ISequence<IAnyUriItem> retval;
-    if (item instanceof IDocumentNodeItem) {
-      IAnyUriItem uri = fnDocumentUri((IDocumentNodeItem) item);
-      retval = ISequence.of(uri);
-    } else {
-      retval = ISequence.empty();
-    }
-    return retval;
+    return item instanceof IDocumentNodeItem
+        ? ISequence.of(fnDocumentUri((IDocumentNodeItem) item))
+        : ISequence.empty();
   }
 
   @SuppressWarnings("unused")
@@ -109,16 +104,9 @@ private static ISequence<IAnyUriItem> executeOneArg(@NonNull IFunction function,
 
     INodeItem item = arg.getFirstItem(true);
 
-    ISequence<IAnyUriItem> retval;
-    if (item == null) {
-      retval = ISequence.empty();
-    } else if (item instanceof IDocumentNodeItem) {
-      IAnyUriItem uri = fnDocumentUri((IDocumentNodeItem) item);
-      retval = ISequence.of(uri);
-    } else {
-      retval = ISequence.empty();
-    }
-    return retval;
+    return item instanceof IDocumentNodeItem
+        ? ISequence.of(fnDocumentUri((IDocumentNodeItem) item))
+        : ISequence.empty();
   }
 
   /**
diff --git a/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/impl/StreamSequence.java b/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/impl/StreamSequence.java
index 75b82e861..d4c840bfd 100644
--- a/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/impl/StreamSequence.java
+++ b/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/impl/StreamSequence.java
@@ -62,6 +62,7 @@ public List<ITEM> getValue() {
   @Override
   public Stream<ITEM> stream() {
     @NonNull Stream<ITEM> retval;
+    // Ensure thread safety and prevent multiple consumptions of the stream
     synchronized (this) {
       if (list == null) {
         if (stream == null) {
diff --git a/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/item/function/IArrayItem.java b/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/item/function/IArrayItem.java
index fa98e22bc..754d186e0 100644
--- a/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/item/function/IArrayItem.java
+++ b/core/src/main/java/gov/nist/secauto/metaschema/core/metapath/item/function/IArrayItem.java
@@ -55,6 +55,15 @@
 
 import edu.umd.cs.findbugs.annotations.NonNull;
 
+/**
+ * A representation of a Metapath array item type.
+ * <p>
+ * Instances of this interface are required to enforce non-mutability for array
+ * contents.
+ *
+ * @param <ITEM>
+ *          the Metapath item type of array members
+ */
 @SuppressWarnings("PMD.ShortMethodName")
 public interface IArrayItem<ITEM extends ICollectionValue> extends IFunction, IItem, List<ITEM>, IStringValued {
   @NonNull