There are many considerations of course and I might not have fully grasped your point, but in reference to your last paragraph: By default RE2 matches directly

There are many considerations of course and I might not have fully grasped your point, but in reference to your last paragraph: By default RE2 matches directly against the UTF-8 encoding, see this neat state diagram: https://swtch.com/~rsc/regexp/regexp3.html#step3 https://swtch.com/~rsc/regexp/regexp3.html#step3 In terms of backtracing engines, perl also stores strings internally as UTF-8 (on most platforms) and its regexp engine runs directly on them. It can also match "eXtended grapheme clusters" with \X.