Return the unicode XML snippet for the ``<c:val>`` element describing
        this series, containing the series values and their spreadsheet range
        reference.

def val_xml(self):
        """
        Return the unicode XML snippet for the ``<c:val>`` element describing
        this series, containing the series values and their spreadsheet range
        reference.
        """
        return self._val_tmpl.format(**{
            'nsdecls':       '',
            'values_ref':    self._series.values_ref,
            'number_format': self._series.number_format,
            'val_count':     len(self._series),
            'val_pt_xml':    self._val_pt_xml,
        })