def unhandledSubnegotiation(command, data):
        """
        A subnegotiation command was received but not understood.

        @param command: the command being subnegotiated. That is, the first
            byte after the SB command.
        @type command: L{str}, a single character.
        @param data: all other bytes of the subneogation. That is, all but the
            first bytes between SB and SE, with IAC un-escaping applied.
        @type data: L{bytes}, each a single character
        """

        A subnegotiation command was received but not understood.

        @param command: the command being subnegotiated. That is, the first
            byte after the SB command.
        @type command: L{str}, a single character.
        @param data: all other bytes of the subneogation. That is, all but the
            first bytes between SB and SE, with IAC un-escaping applied.
        @type data: L{bytes}, each a single character
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/telnet.py