How does it compare with https://github.com/servo/html5ever (someone with free time do run some benchmarks)

That's a great question, and fits nicely in the context of the current discussion.

I think the primary claim to fame for this C-based https://github.com/kovidgoyal/html5-parser is serving as a drop-in performance boost for lxml (at the API level; it parses invalid HTML differently/more consistently).

I too would be interested in a performance comparison to help decide which project makes more sense for new projects. The existing Python layer in html5-parser might give it a leg up if the language of choice is Python - is there a similar project for the Rust-based html5ever?