Comment 1 for bug 855516

Ideally we should use _NET_WM_STATE_FOCUSED rather than _NET_ACTIVE_WINDOW for determining which window is logically active.

http://mail.gnome.org/archives/wm-spec-list/2011-October/msg00000.html

_NET_WM_STATE_FOCUSED allows window managers to specify which window(s) are logically in focus rather than _NET_ACTIVE_WINDOW which is restricted to which window has the input focus, which we can't just change whenever we want for various reasons. Compiz still needs support for this, I'm pretty sure I added it in last week but I haven't had a chance to test it yet.