A client attaches a file to an entity of the application (an upload's attachment): edms cannot know who may, the application answers. Nobody answering lets it; a listener answering false refuses it (a 403).
class MMO\edms\events\Attach extends MMO\core\events\Signal
Collect every listener for this class, including those registered on its parent classes (so a subclass event is also caught by listeners of its parent event), sorted by ascending $order (ties keep …
Change the order of an already-registered listener, whether added directly via AddListener or indirectly via ConnectListeners (which also stores its [$obj, $methodName] callables here).