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@@ -153,3 +153,11 @@ A good heuristic for whether a use case fits this NIP is whether labels would ev
 For example, many events might be labeled with a particular place, topic, or pubkey, but labels
 with specific values like "John Doe" or "3.18743" are not labels, they are values, and should
 be handled in some other way.
+
+
+Appendix: Known Ontologies
+-------------------------
+
+Below is a non-exhaustive list of ontologies currently in widespread use.
+
+- [social.ontolo.categories](https://ontolo.social/)