Presently there is an impl_ property for the 'treeItemCount' in TreeView and TreeTableView. This integer property essentially represents the number of rows that are visible given the current state of expansion in the control. For example, a root with no children visible will be 1, whereas a root with three leaf children will result in a value of 4. This property was made an impl_ property initially to allow for the API to bake, but now that it is heavily used and works well I think the impl_ should be removed and the related methods (impl_getTreeItemCount() and impl_treeItemCountProperty()) should now be made proper public API.