code: def add_range(self, name, start=None, end=None):
          
          self._ranges.append(_mk_range_bucket(name, 'start', 'end', start, end))
          return self
docs: Adds a date range to the given facet.
  
          :param str name:
              The name by which the results within the range can be accessed
          :param str start: Lower date range. Should be in RFC 3339 format
          :param str end: Upper date range.
          :return: The `DateFacet` object, so calls to this method may be
              chained