code: public function add($elementOrFieldset, array $flags = array())
      {
          parent::add($elementOrFieldset, $flags);
          if ($elementOrFieldset instanceof FormParentInterface) {
              $elementOrFieldset->setParent($this);
          }
          return $this;
      }
docs: @param array|\Traversable|\Zend\Form\ElementInterface $elementOrFieldset
  @param array                                          $flags
  
  @return $this