public function before()
    {
        $this->importNodes(\func_get_args(), function ($node, $imported_node) {
            if ($node->parentNode instanceof \DOMDocument) {
                throw new \Exception('Can not set before root element '.$node->tagName.' of document');
            }

            $node->parentNode->insertBefore($imported_node, $node);
        });

        return $this;
    }