diff --git a/Doc/tutorial/classes.rst b/Doc/tutorial/classes.rst
--- a/Doc/tutorial/classes.rst
+++ b/Doc/tutorial/classes.rst
@@ -692,16 +692,21 @@ breaking intraclass method calls.  For e
    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)
 
+The above example would work even if ``MappingSubclass`` were to introduce a
+``__update`` identifier since it is replaced with ``_Mapping__update`` in the
+``Mapping`` class  and ``_MappingSubclass__update`` in the ``MappingSubclass``
+class.
+
 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.
 
 Notice that code passed to ``exec()`` or ``eval()`` does not consider the
 classname of the invoking class to be the current class; this is similar to the
 effect of the ``global`` statement, the effect of which is likewise restricted
 to code that is byte-compiled together.  The same restriction applies to