diff -r 47d0843647d1 -r 4edd179fefb8 mercurial/branchmap.py
--- a/mercurial/branchmap.py	Sun Jan 12 23:28:21 2014 +0100
+++ b/mercurial/branchmap.py	Thu Nov 21 15:17:18 2013 -0500
@@ -167,6 +167,8 @@
             return False
 
     def _branchtip(self, heads):
+        '''Return tuple with last open head in heads and false,
+        otherwise return last closed head and true.'''
         tip = heads[-1]
         closed = True
         for h in reversed(heads):
@@ -177,6 +179,9 @@
         return tip, closed
 
     def branchtip(self, branch):
+        '''Return the tipmost open head on branch head, otherwise return the
+        tipmost closed head on branch.
+        Raise KeyError for unknown branch.'''
         return self._branchtip(self[branch])[0]
 
     def branchheads(self, branch, closed=False):