anchor.diff:     * Fired when the user ends the dragging. 
      * 
      * Is also fired when the user clicks the 'esc'-key or the window loses focus. 
  -   * For those two cases, the mouse positions of [DragEvent] will be null.
      */
     Stream<DragEvent> get onDragEnd => _dragDetector.onDragEnd;
     
  
positive.code:         disableMouse: disableMouse, 
          handle: handle,
          cancel: cancel,
          draggingClassElement: draggingClassSwiper, 
          draggingClassBody: draggingClassBody);
      
      // Swiping is only done horizontally.
      _dragDetector.horizontalOnly = true;
      
      // Listen for drag events.
      _subs.add(_dragDetector.onDragStart.listen(_handleDragStart));
  
negative.code:  * A touch and mouse slider for swiping through images and html.
   */
  class Swiper {
    
    // -------------------
    // Events
  