public function addTypes($types)
    {
        if ($types instanceof DomDocument) {
            $dom = $this->_dom->importNode($types->documentElement);
            $this->_wsdl->appendChild($types->documentElement);
        } elseif ($types instanceof DomNode || $types instanceof DomElement || $types instanceof DomDocumentFragment) {
            $dom = $this->_dom->importNode($types);
            $this->_wsdl->appendChild($dom);
        }
    }