HTML5 validator
The Nu Html Checker (v.Nu) is the backend of checker.html5.org,
html5.validator.nu, and validator.w3.org/nu. It can be used to batch-check
HTML 5 documents from the command line and from other scripts/apps, or
deployed as a self-contained web service.

Maintainer: Anthony J. Bentley <bentley@openbsd.org>

WWW: https://validator.github.io/validator/
