public static function getInstance()
 {
     if (is_null(self::$instance)) {
         self::$instance = new em_MenuMeta_Engine();
     }
     return self::$instance;
 }
 function start_el(&$output, $item, $depth = 0, $args = array(), $id = 0)
 {
     $item_output = '';
     parent::start_el($item_output, $item, $depth, $args, $id);
     $output .= preg_replace('/(?=<p[^>]+class="[^"]*field-move)/', em_MenuMeta_Engine::getInstance()->generate_field($item, $depth, $args), $item_output);
 }