WINDOW_INTERNAL_P 3673 src/window.c         if (WINDOW_INTERNAL_P (w))
WINDOW_INTERNAL_P 3707 src/window.c         if (WINDOW_INTERNAL_P (w))
WINDOW_INTERNAL_P  587 src/window.h     (WINDOW_INTERNAL_P (W) && (W)->horizontal)
WINDOW_INTERNAL_P  591 src/window.h     (WINDOW_INTERNAL_P (W) && !(W)->horizontal)