def define_charset(self, code, mode):
        """Define ``G0`` or ``G1`` charset.

        :param str code: character set code, should be a character
                         from ``"B0UK"``, otherwise ignored.
        :param str mode: if ``"("`` ``G0`` charset is defined, if
                         ``")"`` -- we operate on ``G1``.

        .. warning:: User-defined charsets are currently not supported.
        """
        if code in cs.MAPS:
            if mode == "(":
                self.g0_charset = cs.MAPS[code]
            elif mode == ")":
                self.g1_charset = cs.MAPS[code]
Define ``G0`` or ``G1`` charset.

        :param str code: character set code, should be a character
                         from ``"B0UK"``, otherwise ignored.
        :param str mode: if ``"("`` ``G0`` charset is defined, if
                         ``")"`` -- we operate on ``G1``.

        .. warning:: User-defined charsets are currently not supported.