Inline CSS Pseudo-classes

Question

I have always thought that you cannot add in-line :hover{..} styles to a element, however I came across this page not that long ago, where I se

Answer 1

As a matter of fact, the same document was referenced in another question here. This is what I had to say about it:

That document you link to is a 10-year-old draft.

It's 11 years old now, but that's not the point (although it does suggest a very likely reason why the example you give doesn't work). The point is that the example given does not appear in the latest revision of the same specification. So, supposedly, embedding selectors in style attributes was deemed not viable and dropped as a result.

My answer to the question linked in the comments suggests why such a feature was deemed not viable — it's simply not compatible with the current state of CSS as a language:

Note that inline styles participate in the same cascade as selectors in rule sets, and take highest precedence in the cascade (!important notwithstanding). So they take precedence even over pseudo-class states. Allowing pseudo-classes or any other selectors in inline styles would possibly introduce a new cascade level, and with it a new set of complications.

Of course, I don't claim to speak for the people who actually made the decisions and/or wrote the spec, but if I were one of them, that's the reason I would have given for not supporting the feature.

That would also explain why no browser has implemented such a feature (or, more likely, the lack of implementation was among the factors causing it to be reconsidered and then ultimately dropped, giving vendors even more of a reason not to start implementing it now that the spec has reached CR status).

The lesson here is to never cite old revisions of W3C technical documents as canon. Always remember to review the latest specification; you should be able to find a link in the header of the document.