The documentation is in RST format in the Doc/ directory. For basic stuff, you can just copy the syntax from existing text, or see e.g. <https://docs.python.org/devguide/documenting.html#restructuredtext-primer> for more hints. For this change, I think we need to mention in Doc/library/ctypes.rst:

* the special AIX changes for find_library(); include “.. versionchanged::” (or maybe versionadded? I’m not sure) notice
* the change for the CDLL constructor, also with versionchanged

Perhaps also add an entry to Doc/whatsnew/3.6.rst.

Patch 160823 does not addressed many of my previous comments. Please have a closer look. I can make simple changes to simplify the code myself, but I don’t really know what to do about the questionable regular expressions, for instance.

Also, see <https://bugs.python.org/issue26439#msg268885>. What was wrong with the cases supported by your original patches?