anchor.diff:        this.lowerAngle: 0.0,
         this.upperAngle: 0.0,
         this.enableLimit: false,
  +      PhysicsJointBreakCallback breakCallback,
         double breakingForce
  -    }) : super(bodyA, bodyB, breakingForce) {
  +    }) : super(bodyA, bodyB, breakingForce, breakCallback) {
       _completeCreation();
     }
   
  
positive.code: part of skysprites;
  
  abstract class PhysicsJoint {
    PhysicsJoint(this._bodyA, this._bodyB, this.breakingForce) {
      bodyA._joints.add(this);
      bodyB._joints.add(this);
    }
  
negative.code:     this.anchorA,
      this.anchorB, {
        double breakingForce,
        PhysicsJointBreakCallback breakCallback,
        this.length,
        this.dampening: 0.0,
        this.frequency: 0.0
      }
    ) : super(bodyA, bodyB, breakingForce, breakCallback) {
      _completeCreation();
    }
  
  