Hi,
Sounds cool

I wonder, how do you add children in XML then?
I suppose you removed the "tabControl" from
the WindowContext::acceptsWindowAsChild method, in order to allow adding it?
In order to make tabs visible and saved to your files, look at the following:
For the tree view, take a look at the method "ManagerDlg::initLayoutTree", where you will see that "__auto_" windows are being denied. (I suppose that tabs are tagged like that as well, right?).
For saving, take a loot at the method "CCELayoutEditorDoc::saveWindow", which also denies the automatic children.
Good luck!