Check whether the given Unicode string contains reserved characters.

        :param string ustring: the string to be checked

def _check_reserved_characters(self, ustring):
        """
        Check whether the given Unicode string contains reserved characters.

        :param string ustring: the string to be checked
        """
        forbidden = [c for c in gc.CONFIG_RESERVED_CHARACTERS if c in ustring]
        if len(forbidden) > 0:
            self._failed(u"The given string contains the reserved characters '%s'." % u" ".join(forbidden))