[regarding the x] and [prior named object]

By cracking open the English Language extension and some tinkering, I currently believe that [regarding the banana] sets [the prior named object] to be the banana. Is that how it works?

§14.5 says

but I’m not sure how to retrieve “the subject” afterwards.

Yes, it sets “prior named object”. It also sets an internal variable for the list count (1).

If you write [regarding 5], it sets the list count to 5 and “prior named object” to “nothing”.

There are also variations like [regarding all open doors].