Extensions provide a possibility to extend certain aspects of a solution or a language, which are not covered by the standard language aspects and the plugin mechanisms. Typically you may need your language to slightly alter its behavior depending on the distribution model - MPS plugin, IntelliJ IDEA plugin or a standalone IDE. In such cases you define your extension points as interfaces to which then different implementations will be provided in different distributions.
Support for extensions exists in
Create an extension point
Create one or more extensions
Both the extension point and the extension must be in the plugin model
Each extension must provide a get method, returning an object
Each extension may opt to receive the activate/deactivate notifications
An extension may declare fields, just like classes can
The language jetbrains.mps.lang.extension declares concepts necessary for building extensions.
The ExtensionPoint concept represents an extension point. The extension object type must be specified as a parameter.
The Extension concept is used to create a concrete extension.
Accessing extension point
An extension point can be accessed by reference using extension point expression.
Accessing extension objects
An extension point includes a way to access all objects provided by its extensions.
Extension points and extensions are managed by the ExtensionRegistry core component.