public function onText($regexp, \Closure $handler)
    {
        $this->managers[] = new Manager(function (Event $event) use ($regexp) {
            return (
                $event instanceof \Viber\Api\Event\Message
                && $event->getMessage() instanceof \Viber\Api\Message\Text
                && preg_match($regexp, $event->getMessage()->getText())
            );
        }, $handler);

        return $this;
    }