Earlier quoted context omitted.
Languages invented after Perl will generally use some flavor of Perl regex syntax, but there are always some minor differences. The issue of the meaning of `$` and changing it via multi-line mode is usually consistent though.
I like to think of "whatever browsers do in js" as an updated common baseline. Whatever your regex engine does, describe it as a delta to the js precedent. That thing is just so ubiquitous. I do wonder though what's the highest number of different regex syntaxes I've ever encountered (perhaps written?) within a single line: bash, grep and sed are never not in a "hold my beer" mood!
That seems like just a web front-end developer’s perspective.