http://tronche.com/gui/x/icccm/sec-4.html#s-4.1.7
> Clients using the Globally Active model can only use a SetInputFocus request
> to acquire the input focus when they do not already have it on receipt of one
> of the following events:
> * ButtonPress
> * ButtonRelease
> * Passive-grabbed KeyPress
> * Passive-grabbed KeyRelease
Since managing a window happens on a MapNotify (which is absent from this
list), the window cannot accept input focus, so we should not try to focus
the window at all.
Fixes an issue with xfce4-notifyd which (correctly) declines focus when
we send WM_TAKE_FOCUS, which puts i3 in a state where i3 focus and X
focus are different when a notification appears.
If input focus is set by the window manager, it is not necessary to send
WM_TAKE_FOCUS because it has already taken focus.
http://tronche.com/gui/x/icccm/sec-4.html#s-4.1.7
> The goal is to support window managers that want to assign the input
> focus to a top-level window in such a way that the top-level window
> either can assign it to one of its subwindows or can decline the offer
> of the focus. For example, a clock or a text editor with no currently
> open frames might not want to take focus even though the window
> manager generally believes that clients should take the input focus
> after being deiconified or raised.
Both setting input focus and sending WM_TAKE_FOCUS is effectively
setting focus on the window twice which is certainly against the spirit
of the spec, if not the letter.
fixes#1167
Tony Crisci