protected function __trigger()
 {
     $xml = new XMLelement('shopping-cart');
     if ($_GET['cart-action']) {
         $action = $_GET['cart-action'];
     } else {
         list($action) = array_keys($_POST['cart-action']);
     }
     if (!method_exists($this, $action)) {
         $this->_error = true;
         $this->_msg = __('Unaccepted action');
     }
     if (!$this->_error) {
         $this->_s =& $_SESSION[__SYM_COOKIE_PREFIX_ . 'cart'];
         $this->{$action}();
     }
     $xml->setAttributeArray(array('action' => General::sanitize($action), 'result' => $this->_error == true ? 'error' : 'success'));
     $xml->appendChild(new XMLElement('msg', $this->_msg));
     return $xml;
 }