diff --git a/README.md b/README.md
index f5996a3..e4f4d99 100644
--- a/README.md
+++ b/README.md
@@ -39,3 +39,6 @@ a calendar server
 - Calendaring Extensions to WebDAV (CalDAV): [RFC 4791](https://datatracker.ietf.org/doc/html/rfc4791)
 - Scheduling Extensions to CalDAV: [RFC 6638](https://datatracker.ietf.org/doc/html/rfc6638)
   - not sure yet whether to implement this
+- Collection Synchronization WebDAV [RFC 6578](https://datatracker.ietf.org/doc/html/rfc6578)
+  - We need to implement sync-token, etc.
+- This is important for more efficient synchronisation