diff -r c83ad57627ae -r a232e6744ba3 mercurial/repository.py
--- a/mercurial/repository.py	Fri Aug 03 12:35:23 2018 -0700
+++ b/mercurial/repository.py	Fri Aug 03 11:02:34 2018 -0700
@@ -15,6 +15,10 @@
     interfaceutil,
 )
 
+# When narrowing is finalized and no longer subject to format changes,
+# we should move this to just "narrow" or similar.
+NARROW_REQUIREMENT = 'narrowhg-experimental'
+
 class ipeerconnection(interfaceutil.Interface):
     """Represents a "connection" to a repository.