anchor.diff:      couldBeOpened.addAll(_rootNodes);
       while (couldBeOpened.isNotEmpty) {
         LogicalRow next = couldBeOpened.removeFirst();
  -      if (previouslyOpened.contains(next.id)) {
  +      if (_previouslyOpened.contains(next.id)) {
           next.click();
           couldBeOpened.addAll(next.children);
         }
  
positive.code:       }
      }
  
      this.previouslyOpened = openedPaths;
  
      _rootNodes.clear();
      this.children.clear();
  
negative.code:   // before the json was reloaded.  Storing this information
    // makes it possible to re-open the tree to where it
    // was before.
    Set<String> _previouslyOpened = new Set<String>();
  
    TreeTable.created() : super.created() {}
  
  