anchor.diff:    }
     
     /**
  +   * Deselects all items. No events are fired.
  +   */
  +  void clearSelection() {
  +    selectedItems.forEach((el) => el.selected = false);
  +  }
  +  
  +  /**
      * Selects all items of the tree that satisfy the predicate [test]. All 
      * previously selected items are deselected. The tree is expanded so that all 
      * selected items are shown. No events are fired.
  
positive.code:       item.selected = true;
        ensureVisible(item);
      });
    }
    
    /**
  
negative.code:    * The returned list contains all items that were selected.
     */
    List<TreeItem> selectWhere(bool test(TreeItem item)) {
      clearSelection();
      
      // Find the items in the tree.
      List<TreeItem> foundItems = findItems(test);
  