This NIP is not yet in main. Here is an overview of PRs referencing this NIP. 
merge nips 12, 16, 20 and 33 into nip 01 MERGED @fiatjaf
Wordsmith 53.md CLOSED @git-sgmoore
Fix event kind in example in NIP 53 MERGED @benthecarman
NIP-53 Live Activities MERGED @vitorpamplona
NIP-53 - Nostr-based domain registration system OPEN @leandro21b