diff -r b7abf0590e1c Doc/library/functions.rst
--- a/Doc/library/functions.rst	Tue May 10 00:38:00 2011 +0200
+++ b/Doc/library/functions.rst	Tue May 10 17:42:53 2011 -0400
@@ -373,7 +373,13 @@
    current scope.  If only *globals* is provided, it must be a dictionary, which
    will be used for both the global and the local variables.  If *globals* and
    *locals* are given, they are used for the global and local variables,
-   respectively.  If provided, *locals* can be any mapping object.
+   respectively.  If provided, *locals* can be any mapping object.  When
+   the code contains only the first expression after :keyword:`in` or the same
+   dictionary is used for both the global and local variables, the code is executed
+   in a new top-level scope.  However, when two different objects are used for the
+   global and local variables, the code is executed as if it were in a class
+   statement in a new top-level scope.
+ 
 
    If the *globals* dictionary does not contain a value for the key
    ``__builtins__``, a reference to the dictionary of the built-in module