public function setMessage($messages, $severity = 'info', $once = false)
    {
        if (!empty($messages)) {
            foreach (gplcart_array_flatten((array) $messages) as $message) {
                if ($once) {
                    $this->session->setMessage($message, $severity);
                } else {
                    $this->data['_messages'][$severity][] = $message;
                }
            }
        }
    }