@neauoire X11 doesn't keep track of focus history, you would have to hook yourself to the FocusIn event and keep track yourself.
@marmarta So you mean, that when the window(ex, firefox) looses focus to focus on the new one(my program), I could record what that one is?
Gregory's Server
@marmarta So you mean, that when the window(ex, firefox) looses focus to focus on the new one(my program), I could record what that one is?