A mask that defines which categories this physics body belongs to.
- iOS 8.0+
- macOS 10.10+
- tvOS 9.0+
- watchOS 3.0+
Every physics body in a scene can be assigned to one or more categories, each corresponding to a bit in the bit mask. You define the mask values used in your game. Use this property together with the
contact properties to define which physics bodies interact with each other and when your game is notified of interactions.