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

[Eli Zaretskii <eliz@gnu.org>]

> From: Jean-Christophe Helary <jean.christophe.helary@gmail.com>
> Date: Mon, 5 Jun 2017 09:33:37 +0900
> Cc: michael.albinus@gmx.de,
>  26925@debbugs.gnu.org,
>  stephen.berman@gmx.net
> 
> It is not about me being happy or not, but about me learning what's correct and what is not. If you tell me that it is not correct to worry about various styles being used seemingly at random, then I learn from that. If you tell me that it is not necessary, which you did, then I can argue that I feel better if the few lines I was involved with are tidied up.

I'm not sure I understand the last sentence, but if I do, then no, you
shouldn't worry about random changes of style, as long as the text is
accurate and is correct English.  This is, after all, descriptive
text in plain English, not a formal document.

> >> No, because in the function signature they are defined as optional.
> > 
> > And yet we usually do say explicitly in doc strings that optional
> > arguments are optional.
> 
> Does that mean that you suggest we explicitly declare them optional in split-string ?

Yes, I think so.