code: def _insert_dLbl_in_sequence(self, idx):
          
          new_dLbl = self._new_dLbl()
          new_dLbl.idx.val = idx
  
          dLbl = None
          for dLbl in self.dLbl_lst:
              if dLbl.idx_val > idx:
                  dLbl.addprevious(new_dLbl)
                  return new_dLbl
          if dLbl is not None:
              dLbl.addnext(new_dLbl)
          else:
              self.insert(0, new_dLbl)
          return new_dLbl
docs: Return a newly created `c:dLbl` element having `c:idx` child of *idx*
          and inserted in numeric sequence among the `c:dLbl` children of this
          element.