anchor.diff:  
     PerformanceStatus get status => parent.status;
     AnimationDirection get direction => parent.direction;
  -  AnimationDirection get curveDirection => parent.curveDirection;
   }
   
   abstract class Evaluatable<T> {
  
positive.code:   SimulationStepper _timeline;
    AnimationDirection get direction => _direction;
    AnimationDirection _direction = AnimationDirection.forward;
    AnimationDirection get curveDirection => _curveDirection;
    AnimationDirection _curveDirection = AnimationDirection.forward;
  
    /// The progress of this performance along the timeline.
    ///
  
negative.code:   ACurve({ this.parent, this.curve, this.reverseCurve }) {
      assert(parent != null);
      assert(curve != null);
      parent.addStatusListener(_handleStatusChanged);
    }
  
    final Animation parent;
  