anchor.diff:          ..attributes.remove('id')
           ..style.cursor = 'inherit';
       
  -    // Set the initial position of avatar.
  -    setLeftTop(draggable.documentOffset);
  -    
       // Ensure avatar has an absolute position.
       avatar.style.position = 'absolute';
       avatar.style.zIndex = '100';
  +    
  +    // Set the initial position of avatar.
  +    setLeftTop(draggable.documentOffset);
       
       // Set pointer-events to none.
       setPointerEventsNone();
  
positive.code:   }
    
    /**
     * Caches the margins of [avatar].
     */
    void _cacheMargins() {
      // Calculate margins.
      var marginEdge = avatar.marginEdge;
      var borderEdge = avatar.borderEdge;
      
      _marginTop = borderEdge.top - marginEdge.top;
      _marginLeft = borderEdge.left - marginEdge.left;
    }
  }
  
  
negative.code:   /// Returns the (cached) top margin of [avatar].
    num get marginTop {
      if (_marginTop == null) {
        cacheMargins();
      }
      return _marginTop;
    }
  