Yes. Chapter 11 "Plugin Development" will cover both plugins and addons.
Griffon supports JavaFX to a certain extent due to:
- mixing Swing and JavaFX with 100% fidelity and with bidirectional communication is not yet possible.
- distributing the runtime jars is forbidden by the license. you're restricted to building applications in webstart and applet modes.
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Building a Better World in your Backyard by Paul Wheaton and Shawn Klassen-Koop