public function getTransformResultsAsElem($dom)
    {
        $transElem = $dom->createElement('transform-results');
        $transElem->setAttribute('apply', $this->apply);
        $prefElem = $dom->createElement('preferred-elements');
        // preferred elements
        foreach ($this->preferredElements as $elem) {
            $element = $dom->createElement('element');
            $element->setAttribute('name', $elem->getElement());
            $element->setAttribute('ns', $elem->getElementNs());
            $prefElem->appendChild($element);
        }
        $transElem->appendChild($prefElem);
        return $transElem;
    }