def xVal(self):
        """
        Return the ``<c:xVal>`` element for this series as an oxml element.
        This element contains the X values for this series.
        """
        xml = self._xVal_tmpl.format(**{
            'nsdecls':    ' %s' % nsdecls('c'),
            'numRef_xml': self.numRef_xml(
                self._series.x_values_ref, self._series.number_format,
                self._series.x_values
            ),
        })
        return parse_xml(xml)
Return the ``<c:xVal>`` element for this series as an oxml element.
        This element contains the X values for this series.