--- a/README	Wed Aug 29 17:23:25 2018 +0200
+++ b/README	Wed Aug 29 17:32:47 2018 +0200
@@ -125,3 +125,7 @@
 In addition, we have compatibility branches to check tests on older version of
 Mercurial. They are the "mercurial-x.y" branches. They are used to apply
 expected test change only, no code change should happen there.
+
+test output change from a changeset in core should adds the following line to their description:
+
+CORE-TEST-OUTPUT-UPDATE: <CORE-NODE-ID>