[PATCH 2 of 2 STABLE V2] revsets: add docs for '%' operator

[Sean Farley]

# HG changeset patch
# User Sean Farley <sean at farley.io>
# Date 1461790938 25200
#      Wed Apr 27 14:02:18 2016 -0700
# Branch stable
# Node ID afb8cf4736582dfbab2a19624c859a2f7855fb44
# Parent  c94d5bcf19875b7b1b04ade9ad2bfb04f80ef1ae
# EXP-Topic doc-only-revset
revsets: add docs for '%' operator

diff --git a/mercurial/help/revsets.txt b/mercurial/help/revsets.txt
--- a/mercurial/help/revsets.txt
+++ b/mercurial/help/revsets.txt
@@ -40,10 +40,15 @@ These are the supported infix operators:
   forms: ``x | y`` and ``x + y``.
 
 ``x - y``
   Changesets in x but not in y.
 
+``x % y``
+  Changesets that are ancestors of x but not ancestors of y (i.e. ::x - ::y).
+  This is shorthand notation for ``only(x, y)`` (see below). The second
+  argument is optional and, if left out, is equivalent to ``only(x)``.
+
 ``x^n``
   The nth parent of x, n == 0, 1, or 2.
   For n == 0, x; for n == 1, the first parent of each changeset in x;
   for n == 2, the second parent of changeset in x.