Browsers have gotten really good at it, but man, have I wasted hours, missed deadlines because of a stray `<li>item2<li>` and such. HTML validity and rapid fee

Browsers have gotten really good at it, but man, have I wasted hours, missed deadlines because of a stray `<li>item2<li>` and such. HTML validity and rapid feedback is just as important as the rapid feedback of unit-tests, a type-checker or a even a linter: it shows you mistakes when you make them, rather than later, when you'll merely run into their effects.