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