I didn't know about <datalist>, but how are you supposed to use it with a non-trivial amount of items in the list? I don't see how this can be a replacement for javascript/XHR based autocomplete.

Don't use it, it totally blows. For another oddity to not use, check out the multiple select: https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/...

Expecting users to press modifiers when clicking on these is so funny.

> I don't see how this can be a replacement for javascript/XHR based autocomplete.

It can't do complex autocomplete. It's ok for simple cases only. I use it with a 25k long list to ease the input. Works well enough for this.

> If we can hand-off any JS functionality to native HTML or CSS, then users can download less stuff, and the remaining JS can pay attention to more important tasks that HTML and CSS can't handle (yet).

You can't. It's only supposed to be used for a limited list.

And even if you allow XHR and add options to a <datalist>, it still has terrible UX.