code: public function parseXml($xml)
  	{
  		if (is_null($xml)) {
  			return null;
  		}
  		$xml = new QuiteSimpleXMLElement($xml);
  		$xml->registerXPathNamespaces($this->namespaces);
  		return $xml;
  	}
docs: Parses an XML-formatted NCIP request or response
  Throws Danmichaelo\QuiteSimpleXMLElement\InvalidXMLException on failure
  
  @param  string   $xml
  @return QuiteSimpleXMLElement