bug#64128: regexp parser zero-width assertion bugs

[Paul Eggert]

On 2023-06-18 13:26, Mattias Engdegård wrote:
> The manual is a bit hazy about what we actually promise, though.
>
> As Paul notes, we must be able to document it and that might not be easy, so 
> perhaps we shouldn't even try (to change, or document)?

Although it's not easy to document, we should do better. I gave that a 
shot by installing the attached patches into the master branch. These 
patches try to document current behavior, including warning about the 
squirrelly behavior you mention. If/when we fix the squirrelly behavior 
we can change that part of the manual accordingly.

The last of the three patches is merely a terminology change: it 
standardizes on the term "bracket expression" for regexps like [a-z]. 
Formerly the doc and comments were inconsistent about the terminology. 
It's better to stick with the POSIX term here, to avoid confusion. I 
myself got confused about this when editing the other two patches.

Comments welcome as usual.

0001-Document-regular-expression-special-cases-better.patch
Description: Text Data

0002-Document-Emacs-vs-POSIX-REs.patch
Description: Text Data

0003-Call-them-bracket-expressions-more-consistently.patch
Description: Text Data