bpo-31968: Documentation -- add clarification on the globals dict for exec() (GH-13140)
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index 7170a78..425a985 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -499,7 +499,8 @@
:func:`exec` function. The return value is ``None``.
In all cases, if the optional parts are omitted, the code is executed in the
- current scope. If only *globals* is provided, it must be a dictionary, which
+ current scope. If only *globals* is provided, it must be a dictionary
+ (and not a subclass of 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. Remember