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.

def _insert_dLbl_in_sequence(self, idx):
        """
        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.
        """
        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