The unicode XML snippet containing the ``<c:pt>`` elements containing
        the values for this series.

def _val_pt_xml(self):
        """
        The unicode XML snippet containing the ``<c:pt>`` elements containing
        the values for this series.
        """
        xml = ''
        for idx, value in enumerate(self._series.values):
            if value is None:
                continue
            xml += (
                '                <c:pt idx="{val_idx:d}">\n'
                '                  <c:v>{value}</c:v>\n'
                '                </c:pt>\n'
            ).format(**{
                'val_idx': idx,
                'value':   value,
            })
        return xml