public function toXML(DOMElement $parent) : DOMElement
    {
        $e = $this->toXMLInternal($parent, Constants::NS_MD, 'md:RequestedAttribute');

        if (is_bool($this->isRequired)) {
            $e->setAttribute('isRequired', $this->isRequired ? 'true' : 'false');
        }

        return $e;
    }