[m-rev.] for post-commit review: improve comments in list.m

[Julien Fischer]

Hi Zoltan,

On Thu, 23 Dec 2021, Zoltan Somogyi wrote:

> This started as a way of addressing issues discussed recently
> on m-users, but I found many other places that needed improvement.
>
> For review by anyone.

You forgot to attach the diff.

Julien.