internal static ExtDelegate AddExtension(string extName, ExtDelegate extProc) {
     AddExtension(extName, extProc, IntPtr.Zero);
     return extProc;
 }
 internal static ExtDelegate AddExtension(string extName, ExtDelegate extProc, IntPtr extData) {
     if( modID != NoData ){
         NativeMethods.AddExtension( modID, DefaultCmdSpace, CtlCmd.AddExtension,
                                     extData, extName, extProc );
     }
     return extProc;
 }
 internal static void AddExtension( IntPtr hID, IntPtr cmdSpaceID, CtlCmd cmd,
                                    IntPtr data, string txtID, ExtDelegate proc);