public function toXML(DOMElement $parent) : DOMElement
    {
        Assert::notEmpty($this->AuthzService);

        $e = parent::toXML($parent);

        foreach ($this->AuthzService as $ep) {
            $ep->toXML($e, 'md:AuthzService');
        }

        foreach ($this->AssertionIDRequestService as $ep) {
            $ep->toXML($e, 'md:AssertionIDRequestService');
        }

        Utils::addStrings($e, Constants::NS_MD, 'md:NameIDFormat', false, $this->NameIDFormat);

        return $e;
    }