protected function buildTableHeader($keys)
    {
        $headers = array();
        foreach ($keys as $key) {
            $headers[$key] = $key === MethodTable::SCALAR
                ? 'value'
                : \htmlspecialchars($key);
            if ($this->tableInfo['colClasses'][$key]) {
                $headers[$key] .= ' '.$this->markupClassname($this->tableInfo['colClasses'][$key]);
            }
        }
        return '<thead>'."\n"
            .'<tr><th>&nbsp;</th>'
                .($this->tableInfo['haveObjRow'] ? '<th>&nbsp;</th>' : '')
                .'<th>'.\implode('</th><th scope="col">', $headers).'</th>'
            .'</tr>'."\n"
            .'</thead>'."\n";
    }