The authors’ previous article (linked in this one) was about doing this in re2 (https://systemf.epfl.ch/blog/re2-lookbehinds/), and they have a fork with those changes though I don’t know that they have a PR.

> the "purism" of RE2 does fly in the face of practicality to an irksome degree

It’s not purism tho. There are very practical reasons to want an FA-based engine, and if you compromise that to get additional features then the engine is pointless, you could have just used a backtracking engine in the first place.

I couldn't find the link in that page, but the fork is here, and seems to be up-to-date: https://github.com/GerHobbelt/re2

If you need that from Go, you can probably use that to create a fork of this: https://github.com/wasilibs/go-re2