protected function buildDomDocumentFromXml($xml)
    {
        // see the following URL for this trick:
        // http://stackoverflow.com/questions/15223224/how-to-remove-all-namespaces-from-xml-in-php-tags-and-attributes

        $sxe     = new \SimpleXMLElement($xml);
        $dom_sxe = dom_import_simplexml($sxe);

        $dom     = new DOMDocument('1.0');
        $dom_sxe = $dom->importNode($dom_sxe, true);
        $dom->appendChild($dom_sxe);

        /** @var DOMElement $element */
        $element = $dom->childNodes->item(0);


        foreach ($sxe->getDocNamespaces(true) as $name => $uri) {

            $element->removeAttributeNS($uri, $name);
        }

        return $dom;
    }