diff --git a/src/services/syntax/parser.ts b/src/services/syntax/parser.ts
index 7386e6f2f3a..7249afd7328 100644
--- a/src/services/syntax/parser.ts
+++ b/src/services/syntax/parser.ts
@@ -154,6 +154,13 @@ module TypeScript.Parser {
         // TODO: do we need to store/restore this when speculative parsing?  I don't think so.  The
         // parsing logic already handles storing/restoring this and should work properly even if we're
         // speculative parsing.
+        //
+        // When adding more parser context flags, consider which is the more common case that the 
+        // flag will be in.  This should be hte 'false' state for that flag.  The reason for this is
+        // that we don't store data in our nodes unless the value is in the *non-default* state.  So,
+        // for example, more often than code 'allows-in' (or doesn't 'disallow-in').  We opt for 
+        // 'disallow-in' set to 'false'.  Otherwise, if we had 'allowsIn' set to 'true', then almost
+        // all nodes would need extra state on them to store this info.
         var strictMode: boolean = false;
         var disallowIn: boolean = false;