about user time in X domain

_NET_WM_USER_TIME property: this property stores an Xserver time which represents the time of the last user input event received for this window(gdk_x11_set_user_time(GdkWindow *window, guint32 timestamp)).
This property may be used by the window manager to alter the focus, stacking, and/or placement behavior of windows when they are mapped depending on whether the new window was created by a user action or is a "pop-up" window activated by a timer or some other event.

Note that this property is automatically updated by GDK, so gdk_x11_set_user_time should only be used by applications which hanle input events bypassing GDK.