Add documentation.

src/EditorFeatures/Core/Implementation/FindReferences/DefinitionLocation.DocumentDefinitionLocation.cs

@@ -19,6 +19,10 @@ public DocumentDefinitionLocation(DocumentLocation location)
                 _location = location;
             }
 
+            /// <summary>
+            /// Show the project that this <see cref="DocumentLocation"/> is contained in as the
+            /// Origination of this <see cref="DefinitionItem"/>.
+            /// </summary>
             public override ImmutableArray<TaggedText> OriginationParts =>
                 ImmutableArray.Create(new TaggedText(TextTags.Text, _location.Document.Project.Name));
 

src/EditorFeatures/Core/Implementation/FindReferences/DefinitionLocation.cs

@@ -49,6 +49,9 @@ internal static ImmutableArray<TaggedText> GetOriginationParts(ISymbol symbol)
         {
             // We don't show an origination location for a namespace because it can span over
             // both metadata assemblies and source projects.
+            //
+            // Otherwise show the assembly this symbol came from as the Origination of
+            // the DefinitionItem.
             if (symbol.Kind != SymbolKind.Namespace)
             {
                 var assemblyName = symbol.ContainingAssembly?.ToDisplayString(SymbolDisplayFormat.MinimallyQualifiedFormat);