Even if you acknowledge a separation of content/structure and presentation, the layering of new ad-hoc languages (CSS) eg. a different syntactic construct, onto

Even if you acknowledge a separation of content/structure and presentation, the layering of new ad-hoc languages (CSS) eg. a different syntactic construct, onto markup does not follow from that premise at all. Markup attributes were introduced exactly for the purpose of holding rendering properties, eg. everything that isn't directly presented to the viewer. The ideal of "semantic markup" was only proposed once CSS was established, as a way to rationalize this ad-hoc separation after the fact. Now with CSS we have a million DSLs without type checking, huge cognitive deficits, and every single problem imaginable when a new language is bolted on top of another. All because HTML had to be backward-compatible, and evolution of HTML as a markup language was held back due to unrelated organizational problems. This is not a good outcome when SGML has all the power you want for rigorously developing document formats on a very long timescale. Edit: Look at the comments in this thread. They're mostly about "how flexbox works" and how to apply particular CSS grid features. Nobody actually authors content with the intent of structure/presentation separation.