public static function addString(
        DOMElement $parent,
        string $namespace,
        string $name,
        string $value
    ) : DOMElement {
        $doc = $parent->ownerDocument;

        $n = $doc->createElementNS($namespace, $name);
        $n->appendChild($doc->createTextNode($value));
        $parent->appendChild($n);

        return $n;
    }