Add clarification regarding Stoppable interface.

proposed/event-dispatcher-meta.md

@@ -100,7 +100,7 @@ Despite their similarities, the Message and Task pipelines have two distinct wor
 | Must be serializable          | May be serializable
 | May be delayed                | Must be processed immediately
 | Listener order not guaranteed | Listener order is guaranteed
-| All listeners will fire       | Listeners may short-circuit the pipeline
+| All listeners will fire       | Listeners may short-circuit the pipeline (if the Stoppable interface is implemented)
 | One-way communication only    | May be one-way or two-way communication