public function toArray($obj = null)
 {
     $arr = array();
     if (!isset($obj)) {
         $obj = $this->toTree();
     }
     foreach ($obj as $att => $val) {
         if (is_array($val) || is_object($val)) {
             $arr[$att] = Xml_Node::toArray($val);
         } else {
             $arr[$att] = $val;
         }
     }
     return $arr;
 }