diff --git a/hosts/by-name/servo/services/ejabberd.nix b/hosts/by-name/servo/services/ejabberd.nix
index 4f8a2f51f..cb60e86b7 100644
--- a/hosts/by-name/servo/services/ejabberd.nix
+++ b/hosts/by-name/servo/services/ejabberd.nix
@@ -16,7 +16,13 @@
 # - <https://compliance.conversations.im/server/uninsane.org/#xep0352>
 { config, lib, pkgs, ... }:
 
-# XXX: avatar support works in MUCs but not DMs
+# federation/support matrix:
+# - avatars
+#   - nixnet.services: works in MUCs but not DMs (as of 2023 H1)
+#   - movim.eu: works in DMs, MUCs untested  (as of 2023/08/29)
+# - calls
+#   - local: audio, video, works in DMs  (as of 2023/08/29)
+#   - movim.eu: audio, video, works in DMs, no matter which side initiated  (as of 2023/08/30)
 let
   # TODO: this range could be larger, but right now that's costly because each element is its own UPnP forward
   # TURN port range (inclusive)