[m-rev.] for review: document how "next integer" operations handle infinite values

[Julien Fischer]

On Tue, 4 Sep 2018, Julien Fischer wrote:

>
> For review by anyone.
>
> ----------
>
> Document how "next integer" operations handle infinite values.

Any comments on this?  I'd like to get it into to today's rotd build
if possible.

Julien.