 // MARK: - SpriteKit Integration
 public extension PhysicsBody {
 	
-	public var category : PhysicsBodyCategory {
+	var category : PhysicsBodyCategory {
 		get {
 			return PhysicsBodyCategory(rawValue: self.categoryBitMask)
 		}

// MARK: - Decomposing Flags
fileprivate extension PhysicsBodyCategory {
	
	fileprivate var seperatedFlags : Set<PhysicsBodyCategory> {
		var flags = Set<PhysicsBodyCategory>()
		
		for i : UInt32 in 0..<32 {

// MARK: - Built In Categories
public extension PhysicsBodyCategory {
	
	static let none	= PhysicsBodyCategory(rawValue: UInt32.allZeros)
	static let all 	= PhysicsBodyCategory(rawValue: ~UInt32.allZeros)
	
}

// MARK: - Setting Collisions and Contacts
public extension PhysicsBodyCategory {
	
	static func enableCollision(between a: PhysicsBodyCategory, and b: PhysicsBodyCategory) {
		combineSeperatedFlags(compositeA: a, compositeB: b) { (x, y) in
			let previous = PhysicsBodyCategory.collisions[x] ?? Set<PhysicsBodyCategory>()
			let updated = previous.union([y])
