I read the title and thought “this is such a bad take.” I read the post and thought it made some sense.
I’m taking from this that the author is considering navigation and menu items as “content” - this seems like the wrong term entirely. I think this was my initial confusion.
I think of “content” as the actual meat of a blog post, page, article or even comment. Usually paragraphs or sentences, etc. Controlling uppercase with CSS seems bonkers in this context. Those writing content (as I know it) should not ever have to worry about CSS, it’s a different concern.
While the author does acknowledge it’s okay to uppercase when it makes semantic sense, the title terminology says something different. Or maybe I’m crazy and “content” just means anything that is displayed on the screen?
A very common case for all-caps content is going to be stuff like section titles within text. Other ones could include names in citations, figure descriptions, certain types of emphasis for technical terms, and so on.
These often come down to stylistic differences in a way where a new designer reworking your choices of typefaces or design could decide that something now needs small caps, to be title-cased, and so on. For these, you want CSS to be handling things, otherwise a change in design means you now need to re-edit all your content to work with it.
Semantic differences would imply that moving from uppercase to lowercase (or from lowercase to all caps). For example, “getting your PIN stolen” has a different meaning from “getting your pin stolen.” This example is also partly why you can often pick a small-caps font variant, which gives you the uppercase look without impacting the meaning.