The message event is fired on a Window object when the window receives a message, for example from a call to Window.postMessage() from another browsing context. This event is not cancellable and does not bubble. mdn 
Listen for two distinct messages. Debug with shift-click.
CLICK LISTEN sing LISTEN shout CLICK LISTEN sing
Send either message, up to 100 each.
CLICK MESSAGE sing CLICK MESSAGE shout
Sing for a while. Try resetting LISTEN counts.
TICK 25 MESSAGE sing MESSAGE sing MESSAGE sing MESSAGE sing SLEEP MESSAGE sing MESSAGE shout
We model event processing on Eric's work.
Sample event listener and source.
Try with Stream of Points
CLICK LISTEN publishSourceData
Try with About Line Plugin which uses jquery events.
CLICK LISTEN thumb
What if MESSAGE created a persistent stream and left it to be discovered in state?
CLICK MESSAGE points TICK 9 FORWARD 60 TURN 140 FORWARD 60 TURN -100 CLICK TURN -355