NIP-27
Text note references
NIP-27 explains how Nostr references can appear inside note text. A note can include a mention of a person or another note, and clients can turn that reference into a useful link.
This is what makes @mentions and quoted-note references feel natural. Instead of only showing a block of strange encoded text, a client can recognize the reference and help readers open the right profile or conversation.
Read more in the official 27.md NIP document.