diff --git a/schemas/README-EDDN-schemas.md b/schemas/README-EDDN-schemas.md
index b903100..8423755 100644
--- a/schemas/README-EDDN-schemas.md
+++ b/schemas/README-EDDN-schemas.md
@@ -29,7 +29,16 @@ It is best to base any new Schema file on
 contents all Schemas specify a top-level JSON Object with the data:
 
 1. `$schemaRef` - Which Schema (including version) this message is for.
-2. `header` - Object containing mandatory information about the upload;
+2. `$id` - The canonical URL for this schema once it is in live service.
+   1. Remember to have the version as in `journal/1` not `journal-v1.0`.
+   2. Do **NOT** end this with a `#` empty fragment.  This is
+  [documented](https://json-schema.org/draft/2020-12/json-schema-core.html#section-8.2.1)
+  as unnecessary.
+   3. Where there are two separate schemas for the same kind of data, but one
+     is for Journal-sourced, and the other for CAPI-sourced, you should have
+     the "filename" of the schema end with `_<source>`, e.g.
+     `fcmaterials_journal/1` and `fcmaterials_capi/1`.
+3. `header` - Object containing mandatory information about the upload;
     1. `uploaderID` - a unique ID for the player uploading this data.  
        Don't worry about privacy, the EDDN service will hash this with a key
        that is regularly changed so no-one knows who an uploader is in-game.