They do use this https://github.com/water783/nips/blob/nip101/101.md
Discussion
Yep, but secret chats run into the same issue that you have to trust your peer and their relays to not identify you.
nostr:npub1tm99pgz2lth724jeld6gzz6zv48zy6xp4n9xu5uqrwvx9km54qaqkkxn72 implements NIP-17 (gif-wrapped messages)