I'm not sure. I thought I saw it on one of the nostr clients, but then I didn't see it in any of the NIPs in the official list. So, I wasn't sure. Mostly, I'd like to implement it on a client myself, but wondering where the "rules" are for implementing. I suppose nostr is still a wild west, so I should just use another client as an example. If anyone knows of an open source one I could look at for inspiration, that you be awesome. Otherwise, I'll start poking around.