protected static function xmlToArray(\SimpleXMLElement $xml)/*# : array */
    {
        $arr = array();
        foreach ($xml as $element) {
            $tag = $element->getName();
            $ele = get_object_vars($element);
            if (!empty($ele)) {
                $arr[$tag] = $element instanceof \SimpleXMLElement ?
                    static::xmlToArray($element) :
                    $ele;
            } else {
                $arr[$tag] = trim($element);
            }
        }
        return $arr;
    }