code: public function children()
      {
          if ($this->node instanceof NodeList) {
              return $this;
          }
          
          $result = $this->helper->tag(null);
          if ($this->node instanceof Container) {
              $result->append($this->node->getChildNodes());
          }
          return $result;
      }
docs: このオブジェクトの子ノード一覧をあらわす HelperObject を返します.
  @return HelperObject