Comments/naming

src/server/session.ts

@@ -700,6 +700,13 @@ namespace ts.server {
             return definitions.map(def => this.toFileSpan(def.fileName, def.textSpan, project));
         }
 
+        /*
+         * When we map a .d.ts location to .ts, Visual Studio gets confused because there's no associated Roslyn Document in
+         * the same project which corresponds to the file. VS Code has no problem with this, and luckily we have two protocols.
+         * This retains the existing behavior for the "simplified" (VS Code) protocol but stores the .d.ts location in a
+         * set of additional fields, and does the reverse for VS (store the .d.ts location where
+         * it used to be and stores the .ts location in the additional fields).
+        */
         private static mapToOriginalLocation<T extends DocumentSpan>(def: T): T {
             if (def.originalFileName) {
                 Debug.assert(def.originalTextSpan !== undefined, "originalTextSpan should be present if originalFileName is");