> Is the modified version you use a personal version or a well-known fork?
I had a specific thing I needed to do, gumbo-parser was a good match, I poked at it a little and moved on. It started with this[1] commit, then I did some other work locally which was not pushed because google/gumbo-parser is without an owner/maintainer. There are a couple of forks, but no/little adoption it seems.
[1] https://github.com/sebcat/gumbo-parser/commit/c158f8090c2df0...