the kind of crossing that happened (%GDK_NOTIFY_INFERIOR, %GDK_NOTIFY_ANCESTOR, %GDK_NOTIFY_VIRTUAL, %GDK_NOTIFY_NONLINEAR or %GDK_NOTIFY_NONLINEAR_VIRTUAL).
See Implementation
the kind of crossing that happened (%GDK_NOTIFY_INFERIOR, %GDK_NOTIFY_ANCESTOR, %GDK_NOTIFY_VIRTUAL, %GDK_NOTIFY_NONLINEAR or %GDK_NOTIFY_NONLINEAR_VIRTUAL).