@abc.abstractmethod<EOL><INDENT>def get_relative_end_weekday(self):<DEDENT>
return<EOL>
Gets the ending weekday number.

        The weekday is based on the calendar type. On the Gregorian
        calendar, 0 is Sunday.

        :return: the weekday number
        :rtype: ``cardinal``
        :raise: ``IllegalState`` -- ``has_relative_weekday_end_offset()`` is ``false``

        *compliance: mandatory -- This method must be implemented.*