On Wed, Apr 07, 2021 at 07:14:20AM +0200, Marcin Borkowski wrote:
> 
> On 2021-04-03, at 06:11, Drew Adams <drew.adams@oracle.com> wrote:

> > After a command finishes and returns, the command
> > loop normally automatically deactivates the mark.
> > IOW, for the next command the mark is inactive.

[...]

> I think I now know the reason - while experimenting with this and
> studying the docs, I probably found out [...]
>      It seems that its main use is to actually _prevent_ the code
> from deactivating the region _if_ it would do it otherwise, by means of
> _modifying_ the buffer.

In a nutshell: deactivating (i.e. setting to nil) `deactivate-mark'
deactivates the mark-deactivating code. Phew ;-)

Cheers
 - t