This NIP is not yet in main. Here is an overview of PRs referencing this NIP. 
NIP-73 - Expand External Content IDs MERGED @MerryOscar
style: fix header styles in same format MERGED @kehiy
Spreadsheets OPEN @vitorpamplona
NIP-73 - External Content IDs MERGED @MerryOscar
Add reviews NIP OPEN @staab
Draft for NIP-73 meetup communities CLOSED @BrightonBTC