Our list of boolean attributes is outdated; it is missing several boolean attributes from [HTML Attributes](https://html.spec.whatwg.org/multipage/indices.html#attributes-3), includes a `scoped` that isn't even present there, and treats [`hidden`](https://html.spec.whatwg.org/multipage/interaction.html#the-hidden-attribute) as boolean despite the expansion of that attribute to be an enumeration including "until-found" by https://github.com/whatwg/html/commit/f5def65bda4d01a6a1e105fcf13fe45201b4f48a. _Originally posted by @gibson042 in https://github.com/jquery/jquery/pull/5384#discussion_r1445103967_