I think it'd be make more sense to just pass event.

`$(event.currentTarget).data('annotation')` can be called from the onAnchorMouseOver. I'm not sure it's violating clean abstraction to expect that we can call this on whatever `event.currentTarget` is, and get the annotation data.

Either that or we should implement a custom event type, and have the anchor implementation emit that with the annotation(s) attached.

Otherwise, we have this strange call signature of a method that looks like an event handler (`onAnchorMouseover`) taking three arguments instead of just one event argument. That would be more idiomatic signature, IMO.