diff -r 534a9e274d88 Doc/reference/simple_stmts.rst
--- a/Doc/reference/simple_stmts.rst	Thu May 12 07:47:06 2011 +0200
+++ b/Doc/reference/simple_stmts.rst	Thu May 12 11:58:58 2011 -0400
@@ -989,10 +989,15 @@
 :keyword:`exec` statement.
 
 In all cases, if the optional parts are omitted, the code is executed in the
-current scope.  If only the first expression after :keyword:`in` is specified,
+current scope.  If only the first expression after ``in`` is specified,
 it should be a dictionary, which will be used for both the global and the local
 variables.  If two expressions are given, they are used for the global and local
-variables, respectively. If provided, *locals* can be any mapping object.
+variables, respectively. If provided, *locals* can be any mapping object.  When
+the code contains only the first expression after ``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.
 
 .. versionchanged:: 2.4
    Formerly, *locals* was required to be a dictionary.