/**
  * @return Frame
  */
 public function next()
 {
     $ret = $this->_cur;
     if (!$ret) {
         return null;
     }
     $this->_cur = $this->_cur->get_next_sibling();
     $this->_num++;
     return $ret;
 }
 /**
  * @return AbstractFrameDecorator
  */
 function get_next_sibling()
 {
     $s = $this->_frame->get_next_sibling();
     if ($s && ($deco = $s->get_decorator())) {
         while ($tmp = $deco->get_decorator()) {
             $deco = $tmp;
         }
         return $deco;
     } else {
         if ($s) {
             return $s;
         }
     }
     return null;
 }