API.txt: $Id: API.txt,v 1.16 2010-10-11 22:18:22 sdboyer Exp $

This file contains a log of changes to the API.
API Version 2.0
  Remove the deprecated callback-based behavior of the 'defaults' property on
    plugin types; array addition is now the only option. If you need more
    complex logic, do it with the 'process' callback.
  Introduce a global plugin type registration hook and remove the per-plugin
    type magic callbacks.

Versions prior to 2.0 have been removed from this document. See the D6 version
for that information.