--- a/mercurial/help/revisions.txt	Tue Jun 06 22:17:39 2017 +0530
+++ b/mercurial/help/revisions.txt	Sat May 27 10:25:09 2017 -0700
@@ -97,6 +97,7 @@
 
 ``x~n``
   The nth first ancestor of x; ``x~0`` is x; ``x~3`` is ``x^^^``.
+  For n < 0, the nth unambiguous descendent of x.
 
 ``x ## y``
   Concatenate strings and identifiers into one string.