public function toXML(DOMElement $parent) : DOMElement
    {
        $doc = $parent->ownerDocument;

        $e = $doc->createElementNS(Common::NS, 'mdui:Logo');
        $e->appendChild($doc->createTextNode($this->url));
        $e->setAttribute('width', strval($this->width));
        $e->setAttribute('height', strval($this->height));
        if ($this->lang !== null) {
            $e->setAttribute('xml:lang', $this->lang);
        }
        $parent->appendChild($e);

        return $e;
    }