@abc.abstractmethod<EOL><INDENT>def get_week_of_month(self):<DEDENT>
return<EOL>
Gets the week of the month for the interval.

        1 is the first week of the month. -1 is the last week of the
        month. 0 is invalid.

        :return: ``the week interval``
        :rtype: ``integer``
        :raise: ``IllegalState`` -- ``has_weekly_interval()`` is ``false`` or ``has_weekof_month_interval()`` is
        ``false``

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