[PageVisibility] Add hidden and visibilityState to visibilitychange event

The 'visibilitychange' event[0] is currently defined as a simple event, containing no unique attributes.  Is there a reason why the event does not include the 'hidden' and 'visibilityState' attributes?

The particular use case I'm trying to satisfy involves capturing an audit log (click stream) of events that can be analyzed offline.  The visibilitychange event as currently defined doesn't provide any detail about the new state, just that the state changed.  While I could copy these properties from the document into the event, including them as part of the spec is reasonable.  As precedent, the 'hashchange' event[1] includes the URL as an attribute, while a developer could lookup the location manually.

Apologies if this has been previously discussed, a search of the list archives didn't turn up any hits.

-Scott

[0] http://www.w3.org/TR/2012/CR-page-visibility-20120726/#sec-visibilitychange-event
[1] http://www.w3.org/TR/2012/WD-html5-20121025/history.html#event-hashchange