bug#46917: 28.0.50; error when unloading feature after loading elp

[Stefan Monnier]

> ----
> You can also define @dfn{auxiliary methods}, by using one of the
> following values as @var{qualifier}:
> ----
>
> But then listed both the :before (etc) and :extra in the same section,
> when you can use both :extra and :before.

It's because it's supposed to be a "list of qualifiers".
Strictly speaking, the set of possible qualifiers can be changed by
adding a new method to `cl-generic-combine-methods`.


        Stefan