That's different. Those are a data structure defining annotations that are meant to be stored externally. They're not part of an HTML file like PDF annotations are. They're meant more for live collaborative commenting within a shared online space, not for making private portable annotations like PDF does.

And it's not a Chrome thing. I don't think any browsers support it, do they? It's not really clear there's a need for it, when collaborative editors already handle document annotations in their own ways.

So is there a need for it or isn't there?

> That's different. Those are a data structure defining annotations that are meant to be stored externally.

The protocol is a separate standard.

The format is JSON-LD. Putting JSON-LD into HTML isn't a question mark. (There's info at W3C.org about how to do that, too. Not that it's necessary. You can guess what it says.)