diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -624,12 +624,6 @@
 @predicate('commonancestors(set)', safe=True)
 def commonancestors(repo, subset, x):
     """Returns all common ancestors of the set.
-
-    This method is for calculating "::x and ::y" (i.e. all the ancestors that
-    are common to both x and y) in an easy and optimized way. We can't quite
-    use "::head()" because that revset returns "::x + ::y + ..." for each head
-    in the repo (whereas we want "::x *and* ::y").
-
     """
     startrevs = getset(repo, fullreposet(repo), x, order=anyorder)
     if not startrevs: