diff --git a/01.md b/01.md
index 8be85bc..b51fdf0 100644
--- a/01.md
+++ b/01.md
@@ -87,7 +87,7 @@ As a convention, all single-letter (only english alphabet letters: a-z, A-Z) key
 
 Kinds specify how clients should interpret the meaning of each event and the other fields of each event (e.g. an `"r"` tag may have a meaning in an event of kind 1 and an entirely different meaning in an event of kind 10002). Each NIP may define the meaning of a set of kinds that weren't defined elsewhere. This NIP defines two basic kinds:
 
-- `0`: **metadata**: the `content` is set to a stringified JSON object `{name: <username>, about: <string>, picture: <url, string>}` describing the user who created the event. A relay may delete older events once it gets a new one for the same pubkey.
+- `0`: **metadata**: the `content` is set to a stringified JSON object `{name: <username>, about: <string>, picture: <url, string>}` describing the user who created the event. [Extra metadata fields](24.md#kind-0) may be set. A relay may delete older events once it gets a new one for the same pubkey.
 - `1`: **text note**: the `content` is set to the **plaintext** content of a note (anything the user wants to say). Content that must be parsed, such as Markdown and HTML, should not be used. Clients should also not parse content as those.
 
 And also a convention for kind ranges that allow for easier experimentation and flexibility of relay implementation: