Excellent, thank you !

Yes, that is exactly right, although in my mind those sections were, in fact, layers rather than parts of a layer.  Perhaps layers could carry a flag, settable via the GUI, that would allow them to indicate whether they were to be absolutely positioned (the present behaviour) or would automatically position themselves above, below or between other layers ...

OK, answer received from online chat advisor Andrzej — double-click on directory name, then overtype with desired name.

Thank you.

Could you possibly tell me how ?  I have just tried, and still can find no way ...

Splendid news — many thanks !