I once did a test with a user having username "_" and added it to nostr.json. NIP-05 is restricted to these characters `a-z0-9-_.` and are case sensitive https://github.com/nostr-protocol/nips/blob/master/05.md
I once did a test with a user having username "_" and added it to nostr.json. NIP-05 is restricted to these characters `a-z0-9-_.` and are case sensitive https://github.com/nostr-protocol/nips/blob/master/05.md
Also, I think what you may be asking is about the root domain ownership and NIP-05 username. It means you could have a nip with yourname@domain or @domain.com as the root.