think\response\Xml::dataToXml PHP Метод

    protected function dataToXml($data, $item, $id)
    {
        $xml = $attr = '';
        foreach ($data as $key => $val) {
            if (is_numeric($key)) {
                $id && ($attr = " {$id}=\"{$key}\"");
                $key = $item;
            }
            $xml .= "<{$key}{$attr}>";
            $xml .= is_array($val) || is_object($val) ? $this->dataToXml($val, $item, $id) : $val;
            $xml .= "</{$key}>";
        }
        return $xml;
    }