diff --git a/mercurial/revset.py b/mercurial/revset.py
index c1d163ce73949c7a5e552484af101fdf51ad6cfd_bWVyY3VyaWFsL3JldnNldC5weQ==..4644e991a12a1557ad939bf67c5f34db5a6722cc_bWVyY3VyaWFsL3JldnNldC5weQ== 100644
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -1105,6 +1105,7 @@
     hs = set()
     for b, ls in repo.branchmap().iteritems():
         hs.update(repo[h].rev() for h in ls)
+    # XXX We should not be using '.filter' here, but combines subset with '&'
     # XXX We should combine with subset first: 'subset & baseset(...)'. This is
     # necessary to ensure we preserve the order in subset.
     return baseset(hs).filter(subset.__contains__)