It doesn't matter any more, and hasn't for years. Browser tech has been moving faster than validators can keep up. Newly specced features are being polyfilled

It doesn't matter any more, and hasn't for years. Browser tech has been moving faster than validators can keep up. Newly specced features are being polyfilled, etc. Browsers and search crawlers deal with this; probably time for validators to be about something other than the site's static assets.