[External] : Use the characters "+" and "-" in regular expressions

[steve-humphreys]

> Sent: Friday, May 21, 2021 at 4:24 AM
> From: "Yuri Khan" <yuri.v.khan@gmail.com>
> To: steve-humphreys@gmx.com
> Cc: "Jean Louis" <bugs@gnu.support>, "help-gnu-emacs@gnu.org" 
> <help-gnu-emacs@gnu.org>
> Subject: Re: [External] : Use the characters "+" and "-" in regular 
> expressions
>
> On Thu, 20 May 2021 at 21:50, <steve-humphreys@gmx.com> wrote:
>
> > I have settled with
> >
> >   (string-match "^[:blank:]*$" s)
> >
> > This would match only strings with spaces, not sentences with spaces.  What 
> > do you think?
>
> No, that will match lines consisting of colons and letters a, b, k, l,
> and n. To use a named character class, you need double brackets.

Like this then

(string-match "^[[:blank:]]*$" s)