in reality, neither of them make any such claims. And they are not html-like - they're literally html. Especially datastar, which doesnt add any non-html-spec attributes.
Yeah, yeah, they "literally add nothing" except these small things like "custom Javascript-like DSL" (datastar), custom DSL and custom HTTP-headers (htmx).
But it's "just html", so it's all fine
Edit: Oh, don't forget that " Especially datastar, which doesnt add any non-html-spec attributes" in reality ads two custom DSLs. One in the form of HTML attribbutes, and the other in the form of a JS-like DSL:
the spec is literally just data-* (hence the name): you can add whatever you want to it and remain in spec. And they're meant to be read by javascript (like datastar)