private function unserializeElem($menu_elem_xml)
 {
     $label = (string) $menu_elem_xml->label;
     $url = (string) $menu_elem_xml->url;
     $submenu_xml = $menu_elem_xml->submenu->{'menu-elem'};
     $menu_elem = new MenuElem($label, $url);
     if ($submenu_xml) {
         foreach ($submenu_xml as $sub_elem_xml) {
             $sub_id = (string) $sub_elem_xml['id'];
             $sub_elem = $this->unserializeElem($sub_elem_xml);
             $menu_elem->addElem($sub_id, $sub_elem);
         }
     }
     return $menu_elem;
 }