public function render()
    {
        $xml = new SimpleXMLElement(
            '<?xml version="1.0" encoding="UTF-8" ?>
            <rss version="2.0"
                xmlns:content="http://purl.org/rss/1.0/modules/content/"
                xmlns:wfw="http://wellformedweb.org/CommentAPI/"
                xmlns:dc="http://purl.org/dc/elements/1.1/"
                xmlns:atom="http://www.w3.org/2005/Atom"
                xmlns:sy="http://purl.org/rss/1.0/modules/syndication/"
                xmlns:slash="http://purl.org/rss/1.0/modules/slash/"
            />',
            LIBXML_NOERROR | LIBXML_ERR_NONE | LIBXML_ERR_FATAL
        );

        foreach ($this->channels as $channel) {
            $toDom = dom_import_simplexml($xml);
            $fromDom = dom_import_simplexml($channel->asXML());
            $toDom->appendChild($toDom->ownerDocument->importNode($fromDom, true));
        }

        $dom = new \DOMDocument('1.0', 'UTF-8');
        $dom->appendChild($dom->importNode(dom_import_simplexml($xml), true));
        $dom->formatOutput = true;

        return $dom->saveXML();
    }