This NIP is not yet in main. Here is an overview of PRs referencing this NIP.
Clarify wording of NIP-24 OPEN @accursed-rose
Add relay list of kind 3 to NIP-24 MERGED @AsaiToshiya
add nip-24: extra metadata fields MERGED @fiatjaf
NIP-24 Sealed Gift-Wrapped Messages for Private DMs and Small Group Chats OPEN @vitorpamplona
NIP-24: Rich Text Note CLOSED @AsaiToshiya
NIP-24: Private Messages OPEN @jeffthibault
NIP-24: Private Messages CLOSED @jeffthibault
NIP-24: Prevent Data Deletion in Replaceable Events CLOSED @Giszmo