A person might get the impression based on your comments that classes are somehow "for" CSS (they're not) and that using them for some non-CSS use is somehow "w

A person might get the impression based on your comments that classes are somehow "for" CSS (they're not) and that using them for some non-CSS use is somehow "wrong" (it's not). Meanwhile almost everything you're saying here is opposite what the HTML spec says. As I said in my (earlier) response to you: using the "class" attribute for semantic, non-styling purpose is not "overloading" or misusing it. It is simply using it. (Just like the folks who developed CSS were able to get use out of element classes by baking tier-one support for them into their selector language. CSS has no claim to the right and proper use of an attribute that predates CSS.) To argue against this is revisionism. The HTML5 data attributes also aren't a replacement for proper use of the class attribute, either. What the class attribute encodes (surprise) the class that the content belongs to. The data attribute payload encodes a particular value associated with a given key for a particular instance (e.g. the testid payload from your own example). And aside from the use cases being incomparable, the HTML spec says they shouldn't be used the way you're saying.