code: def yVal_xml(self):
          
          return self._yVal_tmpl.format(**{
              'nsdecls':    '',
              'numRef_xml': self.numRef_xml(
                  self._series.y_values_ref, self._series.number_format,
                  self._series.y_values
              ),
          })
docs: Return the ``<c:yVal>`` element for this series as unicode text. This
          element contains the Y values for this series.