ip_diffim's Doxygen settings were modified in 2014 to generate HTML documentation for both public and private members. Because of how the build system handles Doxygen overrides, this change had the (presumably unintended) consequence that the Stack-wide documentation also exposed private class members, whether or not they had documentation comments.

Per RFC-451, the override will be removed, so that both ip_diffim's and the Stack's documentation includes only API members.