Add comments to IResultSetTracker

src/Features/Lsif/Generator/ResultSetTracking/IResultSetTracker.cs

@@ -12,8 +12,23 @@ namespace Microsoft.CodeAnalysis.LanguageServerIndexFormat.Generator.ResultSetTr
     /// </summary>
     internal interface IResultSetTracker
     {
+        /// <summary>
+        /// Returns the ID of the <see cref="ResultSet"/> that represents a symbol.
+        /// </summary>
         Id<ResultSet> GetResultSetIdForSymbol(ISymbol symbol);
+
+        /// <summary>
+        /// Returns an ID of a vertex that is linked from a result set. For example, a <see cref="ResultSet"/> has an edge that points to a <see cref="ReferenceResult"/>, and
+        /// item edges from that <see cref="ReferenceResult"/> are the references for the range. This gives you the ID of the <see cref="ReferenceResult"/> in this case.
+        /// </summary>
         Id<T> GetResultIdForSymbol<T>(ISymbol symbol, string edgeKind, Func<T> vertexCreator) where T : Vertex;
+
+        /// <summary>
+        /// Similar to <see cref="GetResultIdForSymbol{T}(ISymbol, string, Func{T})"/>, but instead of creating the vertex (if needed) and adding an edge, this
+        /// simply tracks that this method has been called, and it's up to the caller that got a true return value to create and add the vertex themselves. This is handy
+        /// when the actual identity of the node isn't needed by any other consumers, or the vertex creation is expensive and we don't want it running under the lock that
+        /// <see cref="GetResultIdForSymbol{T}(ISymbol, string, Func{T})"/> would have to take.
+        /// </summary>
         bool ResultSetNeedsInformationalEdgeAdded(ISymbol symbol, string edgeKind);
     }
 }