code: def set_monthly(self, interval, *, day_of_month=None, days_of_week=None,
                      index=None, **kwargs):
          
          if not day_of_month and not days_of_week:
              raise ValueError('Must provide day_of_month or days_of_week values')
          if day_of_month and days_of_week:
              raise ValueError('Must provide only one of the two options')
          self.set_daily(interval, **kwargs)
          if day_of_month:
              self.__day_of_month = day_of_month
          elif days_of_week:
              self.__days_of_week = set(days_of_week)
              if index:
                  self.__index = index
docs: Set to repeat every month on specified days for every x no. of days
  
          :param int interval: no. of days to repeat at
          :param int day_of_month: repeat day of a month
          :param list[str] days_of_week: list of days of the week to repeat
          :param index: index
          :keyword date start: Start date of repetition (kwargs)
          :keyword date end: End date of repetition (kwargs)
          :keyword int occurrences: no of occurrences (kwargs)