bug#26925: Improve /doc/lispref/strings.texi (split-string) documentation

[Eli Zaretskii]

> From: Jean-Christophe Helary <jean.christophe.helary@gmail.com>
> Date: Sun, 4 Jun 2017 08:45:47 +0900
> Cc: stephen.berman@gmx.net,
>  26925@debbugs.gnu.org
> 
> >> It's up to you. I thought it was weird that all the other optional 
> >> arguments were not labeled as "optional" and only this one.
> > 
> > That's not what I see: grepping the ELisp manual for "optional
> > argument" comes up with more than 200 hits.  It's quite normal to use
> > that.
> 
> I am talking about this function. This function does not use "optional 
> arguments" for its other optional arguments.

Sorry, but I don't see that as a significant evidence.  There's
nothing special about this function that would cause us to treat it
any different from the rest.

Once again, these are matters of personal style, and IMO we shouldn't
make changes motivated by style preferences alone.