Addons are .jar-packaged modules for Quail that can modify Quail behaviour.
They can add:
Addons can be attached with a global flag:
quail -G.addons=path_to_addon_jar
Multiple addons specified as follows
quail -G.addons=path_to_addon1;path_to_addon2
You can find information about how to create addons on Quail Developer Tutorials