docs: def as_tuple(self):
          """Date as three-tuple of numbers"""
          if self._tuple is None:
              # extract leading digits from year
              year = 9999
              if self.year:
                  m = self.DIGITS.match(self.year)
                  if m:
                      year = int(m.group(0))
              month = self.month_num or 99
              day = self.day if self.day is not None else 99
  
              # should we include calendar name in tuple too?
              self._tuple = year, month, day
  
          return self._tuple