code: def set_flagged(self, *, start_date=None, due_date=None):
          
          self.__status = Flag.Flagged
          start_date = start_date or dt.datetime.now()
          due_date = due_date or dt.datetime.now()
          if start_date.tzinfo is None:
              start_date = self.protocol.timezone.localize(start_date)
          if due_date.tzinfo is None:
              due_date = self.protocol.timezone.localize(due_date)
          self.__start = start_date
          self.__due_date = due_date
          self._track_changes()
docs: Sets this message as flagged
          :param start_date: the start datetime of the followUp
          :param due_date: the due datetime of the followUp