/**
* Return the xml string built that we are about to send over to the api
* @return string
*/
protected function getXMLString()
{
// Add in the defaults
$postFields = array('@attributes' => array('USERID' => $this->username));
// Add in the sub class data
$postFields = array_merge($postFields, $this->getPostFields());
$xml = XMLParser::createXML($this->apiCodes[$this->apiVersion], $postFields);
return $xml->saveXML();
}