Document validation: How to run locally?

I have a document PR that doesn't validate:
https://github.com/w3c/webrtc-stats/pull/792

The problem is almost certainly a missing level of tag somewhere - but the
annoyance is that I can't figure out from the repo and the
.github/workflows file how to run the verifier locally so that I can check
that my fix fixes before pushing it.

Help?

Harald