private static function addEventCallbacks(array $events = [])
    {
        $hooks = ['before' => 'ing', 'after' => 'ed'];

        foreach ($events as $event)
        {
            foreach ($hooks as $hook => $suffix)
            {
                $method = $hook . ucfirst($event) . 'e';
                $callback = $event . $suffix;

                self::addObservableEvent($method, $callback);
            }
        }
    }