Why ":" is not allowed in file names?

[Chere Zhou]

in reply_ntcreate_and_X at nttrans.c:

                        /*
                         * Check to see if this is a mac fork of some kind.
                         */

                        if( strchr_m(fname, ':')) {
                                END_PROFILE(SMBntcreateX);
                                return 
ERROR_NT(NT_STATUS_OBJECT_PATH_NOT_FOUND);
                        }

I would like to know why we do not allow ":" in file names?

Thanks,
Chere