public function createNotification($format, $alert, array $options = [], $tagsOrTagExpression = '', \DateTime $scheduleTime = null)
    {
        $class = __NAMESPACE__.'\\'.ucfirst($format).'Notification';

        if (!class_exists($class)) {
            throw new \RuntimeException('Invalid format: '.$format);
        }

        return new $class($alert, $options, $tagsOrTagExpression, $scheduleTime);
    }