diff --git a/book/source/04-certificates.md b/book/source/04-certificates.md
index c083959..fc8903b 100644
--- a/book/source/04-certificates.md
+++ b/book/source/04-certificates.md
@@ -143,13 +143,17 @@ Identity components in an OpenPGP certificate are used by the certificate holder
 
 An OpenPGP certificate can contain any number of [User IDs](https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-10.html#name-user-id-packet-tag-13). Each User ID associates the certificate with an identity.
 
-Often, identities in a User ID consist of a string that is composed of a name and an email address (this string must be UTF-8 encoded).
-
 ```{figure} diag/user_id.png
 
 OpenPGP certificates can contain any number of User IDs
 ```
 
+Often, identities in a User ID consist of a UTF-8 encoded string that is composed of a name and an email address. By convention, User IDs typically consist of an [RFC2822](https://www.rfc-editor.org/rfc/rfc2822) *name-addr*.
+
+Also see [draft-dkg-openpgp-userid-conventions-00](https://datatracker.ietf.org/doc/draft-dkg-openpgp-userid-conventions/), 25 August 2023.
+
+One proposed variant for encoding identities in User ID is to use ["split User IDs"](https://dkg.fifthhorseman.net/blog/2021-dkg-openpgp-transition.html#split-user-ids). 
+
 (primary_user_id)=
 #### Primary User ID and its implications