protected function buildTableFooter($keys)
    {
        $haveTotal = false;
        $cells = array();
        foreach ($keys as $key) {
            $colHasTotal = isset($this->tableInfo['totals'][$key]);
            $cells[] = $colHasTotal
                ? $this->dump(\round($this->tableInfo['totals'][$key], 6), true, 'td')
                : '<td></td>';
            $haveTotal = $haveTotal || $colHasTotal;
        }
        if (!$haveTotal) {
            return '';
        }
        return '<tfoot>'."\n"
            .'<tr><td>&nbsp;</td>'
                .($this->tableInfo['haveObjRow'] ? '<td>&nbsp;</td>' : '')
                .\implode('', $cells)
            .'</tr>'."\n"
            .'</tfoot>'."\n";
    }