diff --git a/README.md b/README.md
index a3926f3..5a444b7 100644
--- a/README.md
+++ b/README.md
@@ -18,3 +18,5 @@ a calendar server
 - [ ] Hiding calendars instead of deleting them
 - [ ] Testing such that I'm confident enough to use it myself :)
 - [ ] WebDAV sync extension [RFC 6578](https://www.rfc-editor.org/rfc/rfc6578)
+  - [ ] implement getctag [see](https://github.com/apple/ccs-calendarserver/blob/master/doc/Extensions/caldav-ctag.txt)
+