Added the HTML5 Validator GitHub Action to the repo of my blog.
It runs after the Jekyll site generation step (and before the deploy-to-server step) to catch invalid HTML syntax.

It is configured to validate all generated pages, and promptly surfaced some invalid HTML.
This was rather surprising, as I manually did run the validation for the blog pages not too long ago.
Turns out when you have a blog with 20 year old comments, then some of them have HTML from 20 years ago which is no longer valid nowadays 🤷

After a round of fixing old comments, all HTML validaton errors are now gone ✅
And future invalid HTML syntax will be alerted upon before it ends up on the Internet 😎