docs: def upcoming_shabbat_or_yom_tov(self):
          """Return the HDate for the upcoming or current Shabbat or Yom Tov.
  
          If it is currently Shabbat, returns the HDate of the Saturday.
          If it is currently Yom Tov, returns the HDate of the first day
          (rather than "leil" Yom Tov). To access Leil Yom Tov, use
          upcoming_shabbat_or_yom_tov.previous_day.
          """
          if self.is_shabbat or self.is_yom_tov:
              return self
  
          if self.upcoming_yom_tov < self.upcoming_shabbat:
              return self.upcoming_yom_tov
          return self.upcoming_shabbat