bug#59559: 28.1; `minibuffer-with-setup-hook' with :append

[Drew Adams]

> > AFAIU FUN is either a function expression or an (unquoted) list
> > (:append FUN) where FUN is a function expression.
>                                ^^^^^^^^^^^^^^^^^^^
> 
> Correction: AFAIR we use that term for "lambda expression or function
> name".  Here any expression is allowed as long as it returns a function,
> so I would just say "expression".

It's maybe not obvious whether, when we use
"expression" we're suggesting that that gets
_evaluated_.

What needs to be made clear here, I think, is
that in (:append F) F is evaluated, and its
value should be a function.  And that function
is invoked (funcalled) with no args.