+ /* Starting in late 2014, GNOME programs don't actually select for
+ or receive KeyPress events: they do it behind the scenes through
+ some kind of Input Method magic, even when running in an en_US
+ locale. However, those applications *do* update the WM_USER_TIME
+ property on their own windows every time they recieve a secret
+ KeyPress, so we must *also* monitor that property on every
+ window, and treat changes to it as identical to KeyPress.
+
+ _NET_WM_USER_TIME is documented (such as it is) here:
+
+ http://standards.freedesktop.org/wm-spec/latest/ar01s05.html
+ #idm139870829932528
+
+ Specifically:
+
+ "Contains the XServer time at which last user activity in this
+ window took place. [...] A client [...] might, for example,
+ use the timestamp of the last KeyPress or ButtonPress event."
+
+ As of early 2016, KDE4 does something really stupid, though: some
+ hidden power management thing reduces the display brightness 150
+ seconds after the screen is blanked -- and sets a WM_USER_TIME
+ property on a hidden "kded4" window whose time is in the distant
+ past (the time at which the X server launched).
+
+ So we ignore any WM_USER_TIME whose timestamp is more than a
+ couple seconds old.
+ */