#7188: fix optionxform() docs.
diff --git a/Doc/library/configparser.rst b/Doc/library/configparser.rst
index ef27524..1af14cc 100644
--- a/Doc/library/configparser.rst
+++ b/Doc/library/configparser.rst
@@ -334,12 +334,20 @@
.. method:: RawConfigParser.optionxform(option)
- Transforms the option name *option* as found in an input file or as passed in by
- client code to the form that should be used in the internal structures. The
- default implementation returns a lower-case version of *option*; subclasses may
- override this or client code can set an attribute of this name on instances to
- affect this behavior. Setting this to :func:`str`, for example, would make
- option names case sensitive.
+ Transforms the option name *option* as found in an input file or as passed in
+ by client code to the form that should be used in the internal structures.
+ The default implementation returns a lower-case version of *option*;
+ subclasses may override this or client code can set an attribute of this name
+ on instances to affect this behavior.
+
+ You don't necessarily need to subclass a ConfigParser to use this method, you
+ can also re-set it on an instance, to a function that takes a string
+ argument. Setting it to ``str``, for example, would make option names case
+ sensitive::
+
+ cfgparser = ConfigParser()
+ ...
+ cfgparser.optionxform = str
.. _configparser-objects: