void UnloadedHandler(object sender, RoutedEventArgs args)
 {
     if (elementModel != null)
     {
         elementModel = null; // have to set to null before clearing bindings
         selectionHelper.Clear();
         BindingOperations.ClearBinding(this, IsExpandedProperty);
     }
 }
 private void UnloadHandler(object sender, RoutedEventArgs e)
 {
     RemoveAdorner();
     selectionHelper.Clear();
     SectionModel = null;
 }