protected function process(ImsXmlReader $item, $_ = '')
 {
     if ($this->break) {
         return;
     }
     if ($item->is_empty()) {
         return;
     }
     $f = array($this, 'process_' . $item->name());
     $args = func_get_args();
     if (is_callable($f)) {
         return call_user_func_array($f, $args);
     } else {
         throw new Exception('Unknown: ' . $item->name());
     }
 }