default boolean propagateTo(@Nullable IConnectable to, @Nullable IPropagationPart prev, int mode) {
        if (to != null) {
            if (to == prev) return false;
            if (to instanceof IPropagationPart part) {
                if (shouldPropagate(part, mode)) {
                    RedstonePropagator.propagateTo(part, this, mode);
                    return true;
                }
            }
        }
        return false;
    }
Provides a 4-bit rotation mask marking sides that will forward-propagate.
core/src/main/java/mrtjp/projectred/core/part/IPropagationFacePart.java