public function render()
 {
     $addons = array();
     if (!empty($this->prepend)) {
         $addons[] = "input-prepend";
     }
     if (!empty($this->append)) {
         $addons[] = "input-append";
     }
     if (!empty($addons)) {
         echo '<div class="', implode(" ", $addons), '">';
     }
     $this->renderAddOn("prepend");
     parent::render();
     $this->renderAddOn("append");
     if (!empty($addons)) {
         echo '</div>';
     }
 }