[whatwg] Fullscreen and keyboard focus.

[João Eiras]

Hi.

Perhaps keyboard focus should be limited only to the fullscreen element or  
its descendants.

If you have a canvas or video fullscreen, alt-tabbing can move the focus  
outside the fullscreen element, say into form elements.

But then this would require giving focus, and dispatching focus events, if  
the focused element is not inside the fullscreen element subtree.