Invo NotFoundPlugin - why abstract dispatcher class is used?

Hi in the NotFoundPlugin of the Invo app is besides Mvc\Dispatcher also the abstract base class used. Could somebody explain please for what reason this is done?

    ...
    use Phalcon\Dispatcher;
    use Phalcon\Mvc\Dispatcher as MvcDispatcher;
    ...
    if ($exception instanceof DispatcherException) {
        switch ($exception->getCode()) {
            case Dispatcher::EXCEPTION_HANDLER_NOT_FOUND:
            case Dispatcher::EXCEPTION_ACTION_NOT_FOUND:
                $dispatcher->forward(
                    [
                        'controller' => 'errors',
                        'action'     => 'show404'
                    ]
                );
                return false;
        }
    }