handle_unknown event publishing policy wrt presence_changed

[bigfleet]

#53 refers to a presence_change event, which I'm interested in tracking, as well.

Is there a reason that this block couldn't publish the event anyway? If no handler is subscribed to the event, isn't it close to a no-op?

Might there be a preference for, say, adding handle_presence_change to this block?

[jimmycuadra]

I'd be happy to have any types of events trigger a custom Lita event that handlers could subscribe to. A PR doing this would gladly be accepted.