/**
  * Constructor
  * 
  * @param HtmlForm $form
  * @return void
  */
 public function __construct(HtmlForm $form)
 {
     $this->_parentForm = $form;
     $tagName = $this->_tagName;
     if ($this->_tagName == '') {
         // decide tag name from tail of class name
         require_once 'core/name_manager.php';
         $parts = NameManager::split(get_class($this));
         $tagName = array_pop($parts);
     }
     parent::__construct($tagName);
 }