--- code/trunk/pcrecpp.h	2008/03/08 17:24:02	326
+++ code/trunk/pcrecpp.h	2009/03/17 10:58:16	390
@@ -646,9 +646,15 @@
   // regexp wasn't valid on construction.
   int NumberOfCapturingGroups() const;
 
-  // The default value for an argument, to indicate no arg was passed in
+  // The default value for an argument, to indicate the end of the argument 
+  // list. This must be used only in optional argument defaults. It should NOT
+  // be passed explicitly. Some people have tried to use it like this:
+  //
+  //   FullMatch(x, y, &z, no_arg, &w);
+  //
+  // This is a mistake, and will not work.
   static Arg no_arg;
-
+  
  private:
 
   void Init(const string& pattern, const RE_Options* options);