anchor.diff:        return;
       }
       
  -    // Ignore clicks from right or middle buttons.
  +    // Only handle left clicks, ignore clicks from right or middle buttons.
       if (startEvent.button != 0) {
         return;
       }
  
positive.code:     
      // Install mouseMove listener.
      _dragSubs.add(document.onMouseMove.listen((MouseEvent event) {
        // Set the current position.
        _currentDrag.position = event.page;
        
  
negative.code:           if (_currentDrag.isScrolling()) {
              // The user is scrolling --> Stop tracking current drag.
              _log.fine('User is scrolling, cancel drag.');
              _handleDragEnd(event);
              return;
            }
            
  