private function startList()
    {
        $this->depth++;

        $values = $this->result->createElement('values');

        // set the key, if applicable
        if (null !== ($key = $this->key())) {
            $values->setAttribute('key', $key);
        }

        $this->current->appendChild($values);

        $this->references[] = $this->current;
        $this->current = $values;
    }