WINDOW_INTERNAL_P 3676 src/window.c         if (WINDOW_INTERNAL_P (w))
WINDOW_INTERNAL_P 3710 src/window.c         if (WINDOW_INTERNAL_P (w))
WINDOW_INTERNAL_P  606 src/window.h     (WINDOW_INTERNAL_P (W) && (W)->horizontal)
WINDOW_INTERNAL_P  610 src/window.h     (WINDOW_INTERNAL_P (W) && !(W)->horizontal)