Merged solution for #11786 from 2.6

Doc/library/configparser.rst

@@ -96,6 +96,9 @@ write-back, as will be the keys within each section.
    This class does not
    support the magical interpolation behavior.
 
+   All option names are passed through the :meth:`optionxform` method.  Its
+   default implementation converts option names to lower case.
+
    .. versionadded:: 2.3
 
    .. versionchanged:: 2.6
@@ -116,10 +119,9 @@ write-back, as will be the keys within each section.
    *defaults*.
 
    All option names used in interpolation will be passed through the
-   :meth:`optionxform` method just like any other option name reference.  For
-   example, using the default implementation of :meth:`optionxform` (which converts
-   option names to lower case), the values ``foo %(bar)s`` and ``foo %(BAR)s`` are
-   equivalent.
+   :meth:`optionxform` method just like any other option name reference.  Using
+   the default implementation of :meth:`optionxform`, the values ``foo %(bar)s``
+   and ``foo %(BAR)s`` are equivalent.
 
    .. versionadded:: 2.3