def starts_within(self, start=None, end=None):
        """
        :return:  normal occurrences that start within the given start and end
        datetimes, inclusive, and drop-in occurrences that 
        """

        qs = self

        if start:
            dt_start=coerce_dt_awareness(start)
            qs = qs.filter(
                Q(is_all_day=False, start__gte=dt_start) |
                Q(is_all_day=True, start__gte=zero_datetime(dt_start))
            )
        if end:
            dt_end=coerce_dt_awareness(end, t=time.max)
            qs = qs.filter(
                # Exclusive for datetime, inclusive for date.
                Q(is_all_day=False, start__lt=dt_end) |
                Q(is_all_day=True, start__lte=zero_datetime(dt_end))
            )

        return qs
:return:  normal occurrences that start within the given start and end
        datetimes, inclusive, and drop-in occurrences that