diff --git a/cchat.go b/cchat.go
index 34f7f2d..cd7de73 100644
--- a/cchat.go
+++ b/cchat.go
@@ -6,6 +6,16 @@
 //
 // Backend
 //
+// Almost anything in the backend comes with an ID. For example, a Server must
+// have an ID, or a Session must have a user ID. The backend is required to
+// guarantee that IDs are somehow unique. This should already be the case for
+// most chat services; for example, Discord provides IDs for guilds, channels,
+// members, and more. The only time that the backend should not guarantee ID
+// uniqueness is across Sessions, because it doesn't make sense to do so. In
+// this case, the frontend should guarantee uniqueness instead, either by
+// discarding duplicated items, overriding them, or anything reasonable and
+// explicit.
+//
 // Methods implemented by the backend that have frontend containers as arguments
 // can do IO. Frontends must NOT rely on individual backend states and should
 // always assume that they will block.
diff --git a/repository/main.go b/repository/main.go
index bc721fa..e4726e3 100644
--- a/repository/main.go
+++ b/repository/main.go
@@ -339,6 +339,17 @@ var Main = Packages{
 
 			Backend
 
+			Almost anything in the backend comes with an ID. For example, a
+			Server must have an ID, or a Session must have a user ID. The
+			backend is required to guarantee that IDs are somehow unique. This
+			should already be the case for most chat services; for example,
+			Discord provides IDs for guilds, channels, members, and more. The
+			only time that the backend should not guarantee ID uniqueness is
+			across Sessions, because it doesn't make sense to do so. In this
+			case, the frontend should guarantee uniqueness instead, either by
+			discarding duplicated items, overriding them, or anything
+			reasonable and explicit.
+
 			Methods implemented by the backend that have frontend containers as
 			arguments can do IO. Frontends must NOT rely on individual backend
 			states and should always assume that they will block.