[MatthiasPortzel]

I would put “check for spec valid HTML” far down the TODO-list. I’m a perfectionist, so I would run the validator at some point, but I find it’s basically never helpful for identifying usability issues with a website. For a non-technical person setting up a personal site, does it really matter?

[berkes]

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.