Obviously, the “Release Notes.txt” and “PluginPackaging.rtf” in the SDK folder are not up-to-date.
The Xojo release notes have more information:
Plugins SDK: Added a way to forward events from a plugin’s NSView to the framework. An example project, HostedPluginExample, has been added to demonstrate how to do this.
Plugins SDK: Enums inside of classes are now supported.
IDE: HTML help can be loaded from ZIP plugins.
IDE: Xojo plugins must be in ZIP format.
Framework: The use of paramarrays no longer causes an error in plugin defined classes.
IDE: Plugins that register methods or events with fully qualified type names (like REALbasic.Rect) for parameters or return types now work correctly.
And Joe adds: Delegates are also supported as of 2013r1