I want to implement an "async select" form element, where values are fetched from the server. Ideally, I'd rather not have to implement an API, but instead update the select DOM with unpoly directly.

Here's an example of what I'm talking about: https://druids.datadoghq.com/components/form/Select#async

I'm not sure what's the right way to implement this with unpoly. I'm thinking about using [up-validate] / [up-watch-event='input'], but I want to make sure this is the proper way of doing it!