That document you link to isn't part of the HTML standard. It seems to be an additional document from the W3C outlining how they'd like people to behave. Conforming to software standards is one thing; you have to do that to make programs work together. But complying with the W3C's wishes on how the web ought to be used is a very different matter. I feel like doing exactly what the W3C says on broader questions is not merely optional, but probably a mistake, considering the people who make it up. It would be like running your company according to a list of "best practices" compiled by a committee at General Motors.