When included in a plug-in script by calling useLibrary("extension"), this library converts that plug-in into an extension plug-in. It must still be packaged as a .seext bundle to be discovered and loaded at the correct time.

The library will define a suitable getPluginType() function on the script's behalf. It will also import a number of classes that are commonly used when writing extension plug-ins.

Extensions are loaded and executed before the program is fully initialized. The variables Editor and Component will be null. However, a valid PluginContext object is provided. Extensions are never "activated" by the user, so they do not require or use a run() function.