This NIP is not yet in main. Here is an overview of PRs referencing this NIP. 
Implement Markdownlint GitHub action OPEN @mariano-perez-rodriguez
Markdown improvements, embelishments, and standardizations CLOSED @mariano-perez-rodriguez
Add links to NIP-21 MERGED @martindsq
Fix typo in NIP-27 MERGED @arthurfranca
Add alternative mention handling NIP MERGED @arthurfranca
NIP-27 Restricted tags CLOSED @Cameri