bug#48058: tab-width's docstring

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Thu, 29 Apr 2021 12:05:39 -0500
> Cc: Gustavo Barros <gusbrs.2016@gmail.com>, 48058@debbugs.gnu.org
> 
> I agree that the docstring is somewhat confusing, as it seems to rule
> out that this variable is ever used to control indentation.  But some
> major modes do precisely that.
> 
> Perhaps we could change the docstring note along the lines of:
> 
>     NOTE: Some major modes use this variable to determine an indentation
>     step, but Emacs itself only uses this to display the width of a TAB
>     character.
> 
> Would something like that make sense?

Something like that, yes.  Perhaps just making the original text less
definitive will do as well.

> Also the last line of the docstring is odd to me:
> 
>     This should be an integer greater than zero.
> 
> Should the "should" be changed to "must"?

Those two are equivalent in this context.