anchor.diff:        _log.finest('DragEnd: deltaX=$deltaX');
         
         // Determine if we are past the threshold.
  -      if (deltaX.abs() > DISTANCE_THRESHOLD) {
  +      if (deltaX.abs() > distanceThreshold) {
           // Determine direction of swipe.
           bool directionRight = deltaX > 0;
           
  
positive.code:    * For those two cases, the mouse positions of [DragEvent] will be null.
     */
    Stream<DragEvent> get onDragEnd => _dragDetector.onDragEnd;
    
    // -------------------
    // Private Properties
  
negative.code:  * A touch and mouse slider for swiping through images and html.
   */
  class Swiper {
    
    // -------------------
    // Options
    // -------------------
    /// How many pixels until a swipe is detected.
    int distanceThreshold = 20;
    
    /// CSS class set to the swiper element while a user is dragging. Default 
    /// class is 'swiper-dragging'. If null, no css class is added.
    String draggingClass = 'swiper-dragging';
  