New offerings by Tim Peters; he writes:

IDLE is now the first Python editor in the Universe not confused by my
doctest.py <wink>.

As threatened, this defines IDLE's is_char_in_string function as a
method of EditorWindow.  You just need to define one similarly in
whatever it is you pass as editwin to AutoIndent; looking at the
EditorWindow.py part of the patch should make this clear.