[Bug libstdc++/116903] c++ regex accepts } and ] as a literal character.

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116903

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Oh right, I always forget that browsers have compatibility features for
ECMAScript regexes:
https://262.ecma-international.org/#sec-additional-ecmascript-features-for-web-browsers

Those are optional for non-browsers.