docs: def _years_in_date_range_within_decade(self, decade, begin_date, end_date):
          """Return a list of years in one decade which is covered by date range."""
          begin_year = begin_date.year
          end_year = end_date.year
          if begin_year < decade:
              begin_year = decade
          if end_year > decade + 9:
              end_year = decade + 9
          return list(range(begin_year, end_year + 1))