src/Event.php
public static function bind($event, $callback, $priority = Event::PRIORITY_NORMAL) {
        $event = strtolower($event);
        self::$handlers[$event][$priority][] = $callback;
        self::$toSort[$event] = true;
    }
public static function bind($event, $callback, $priority = Event::PRIORITY_NORMAL) {
        $event = strtolower($event);
        self::$handlers[$event][$priority][] = $callback;
        self::$toSort[$event] = true;
    }
Bind an event handler to an event.

@param string $event The naame of the event to bind to.
@param callback $callback The callback of the event.
@param int $priority The priority of the event.