anchor.diff:    double constrainDeltaTheta(double deltaTheta) {
       return clamp(min: minDeltaTheta, max: maxDeltaTheta, value: deltaTheta);
     }
  +
  +  bool get isTight => minDeltaTheta >= maxDeltaTheta && minDeltaTheta >= maxDeltaTheta;
   }
   
   class SectorDimensions {
  
positive.code:     return new SectorDimensions.withConstraints(constraints);
    }
  
    SectorConstraints get constraints { SectorConstraints result = super.constraints; return result; }
    void performResize() {
      // default behaviour for subclasses that have sizedByParent = true
      deltaRadius = constraints.constrainDeltaRadius(0.0);
  
negative.code: 
  const double kTwoPi = 2 * math.PI;
  
  class SectorConstraints extends Constraints {
    const SectorConstraints({
      this.minDeltaRadius: 0.0,
      this.maxDeltaRadius: double.INFINITY,
  