code: def get_or_add_dLbl_for_point(self, idx):
          
          matches = self.xpath('c:dLbl[c:idx[@val="%d"]]' % idx)
          if matches:
              return matches[0]
          return self._insert_dLbl_in_sequence(idx)
docs: Return the `c:dLbl` element representing the label of the point at
          index *idx*.