src/Application.php
public function registerSubscriber($class, callable $callback)
    {
        $service_id = "event." . strtolower(str_replace("\\", ".", $class));

        $this[$service_id] = $callback;

        $this["dispatcher"]->addSubscriberService($service_id, $class);
    }
public function registerSubscriber($class, callable $callback)
    {
        $service_id = "event." . strtolower(str_replace("\\", ".", $class));

        $this[$service_id] = $callback;

        $this["dispatcher"]->addSubscriberService($service_id, $class);
    }
register our event subscriber
@param string $class
@param callable $callback