Bug 571390, add a comment

--HG--
extra : rebase_source : 5960b90841cfa37decfb48d61e904c97c9d4f91e

content/base/src/nsGenericElement.h

@@ -662,6 +662,8 @@ public:
     const nsAttrValue* mValue;
   };
 
+  // Be careful when using this method. This does *NOT* handle
+  // XUL prototypes. You may want to use GetAttrInfo.
   const nsAttrValue* GetParsedAttr(nsIAtom* aAttr) const
   {
     return mAttrsAndChildren.GetAttr(aAttr);