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.