Apple Shake 4 - Manual (Page 537)

Chapter 19 Using Masks 537
3 Connect the sign_mask2 node to the Background input (the second input) of the
Outside node.
The light mask is “outside” of the sign mask.
The following example demonstrates the wrong way to combine the sign and
car masks.
m Using the following image as a guide, combine the sign_mask and the car_mask with
an Over (or Max) node.
Outside1 KeyMix1