--- a/mercurial/configitems.py	Fri Apr 13 23:37:53 2018 -0700
+++ b/mercurial/configitems.py	Wed Mar 28 09:36:02 2018 -0700
@@ -590,6 +590,9 @@
 coreconfigitem('experimental', 'revlogv2',
     default=None,
 )
+coreconfigitem('experimental', 'revisions.disambiguatewithin',
+    default=None,
+)
 coreconfigitem('experimental', 'single-head-per-branch',
     default=False,
 )