Alternatively: have the element actually do something by hooking it up to the new Moment API and having it display the specified timestamp in the user's locale. That would at least provide an easy way to have the input format and the display format be the same.

But yes, there's also a very good argument to be made in favor of having such localized elements follow the content's `lang` attribute - potentially with a `lang="initial"` to reset it to "whatever the user has configured for their OS".

I'd be okay with regional date format for the user but it always submits as ISO 8601 date format.

That's already how it works, is it not?

Dealing with this right now. Got some people whose devices are set to display dates as dd/mm/yyyy and the janky pay submission form records it verbatim rather than translate to its internal mm/dd/yyyy format. If it's invalid date it will reject, but a guy submitted for August 4 and got denied for the system recording it as April 8. Spreadsheet MS Forms nonsense. Nobody cares.

Also temperature, weights, distances…