diff -r d1eba2645b80 Doc/tutorial/classes.rst
--- a/Doc/tutorial/classes.rst	Sun Apr 13 23:52:43 2014 -0400
+++ b/Doc/tutorial/classes.rst	Mon Apr 14 12:15:38 2014 +0530
@@ -618,6 +618,21 @@
            for item in zip(keys, values):
                self.items_list.append(item)
 
+The above example would work even if MappingSubclass were to introduce
+``__update`` to its symbol table too, since ``__update`` is replaced with
+``_Mapping__update`` in the ``Mapping`` class  and ``_MappingSubclass__update``
+in the ``MappingSubclass``.  For example:
+
+   class MappingSubclass(Mapping):
+
+       def update(self, keys, values):
+           # provides new signature for update()
+           # but does not break __init__()
+           for item in zip(keys, values):
+               self.items_list.append(item)
+
+       __update = update
+
 Note that the mangling rules are designed mostly to avoid accidents; it still is
 possible to access or modify a variable that is considered private.  This can
 even be useful in special circumstances, such as in the debugger.