Thank you for your help so far.
There are two OpenType Features example files at:
How to make a contextual cursive font - #5 by ErwinDenissen .
I wonder if one of those (probably the second) could be brought up-to-date, as neither FontCreator 15 nor I, can interpret them?
Or is there an alternative example?
I won’t be able to respond immediately as I am going away for a few days.