To be clear, I do not believe ripgrep is faster than grep because it has fewer features. At least, I've yet to see any evidence to the contrary.

I did try to explain why I think ripgrep is faster in all kinds of gory details though. :-)

I don't know about that (as in I haven't looked so I literally don't know). First of all, provided the tools produce identical results for similarly-complex regex patterns I'm not sure having to support all POSIX regexes is necessary. Second of all my point was really that the performance achievement is not nearly as interesting as the level of rust-guaranteed safety found as compared with similar implementations in other ("unsafe") languages.