Update Metadata.h

Author: pgeier

src/multio/message/Metadata.h

@@ -51,7 +51,15 @@ class Metadata : public BaseMetadata {
     using Iterator = typename MapType::iterator;
     using ConstIterator = typename MapType::const_iterator;
 
-    // Onlything we need to change to support lookups in parametrization
+    // The single place we need to change to support lookups in parametrization.
+    // Important: The non-const version will copy values from the global parametrization dictionary 
+    //            to the local one - It will always return an iterator to the local dictionary.
+    //            This allows values to be modified in the local object directly.
+    //        
+    //            The const version will return either an iterator to the local object or the 
+    //            global parametrization dictionary.
+    //            If keys are assumed to hold nested objects or large arrays which won't be modified anyway -
+    //            it is reasonable to explicitly const-cast the object to select the const lookup version.
     Iterator find(const KeyType& k) override;
     ConstIterator find(const KeyType& k) const override;