ags to set on the user or channel.
        @type limit: C{int}
        @param limit: In conjunction with the C{'l'} mode flag, limits the
             number of users on the channel.
        @type user: C{str}
        @param user: The user to change the mode on.
        @type mask: C{str}
        @param mask: In conjunction with the C{'b'} mode flag, sets a mask of
            users to be banned from the channel.
        z