What is the syntax of a comment in a .rgs file

For reasons which I won't go into I am auto-generating a load of .rgs files for a Visual Studio 2008 ATL project. I would like to be able to put a comment into each .rgs file indicating that it was auto-generated, and when, but I can't find out what the comment syntax for a .rgs file is, if indeed there is one. I've tried // ; ;; REM and even # but none of these works. There seems to be a paucity of documentation available for the .rgs file format. Any suggestions anyone?