docs: def _check_changetype(self, dn, changetype, attr_value):
          """Check changetype attribute for issues."""
          if dn is None:
              self._error('Read changetype: before getting valid dn: line.')
          if changetype is not None:
              self._error('Two lines starting with changetype: in one record.')
          if attr_value not in CHANGE_TYPES:
              self._error('changetype value %s is invalid.' % attr_value)