Cleanup

tutorial/extensions.md

@@ -1,26 +1,28 @@
 # Plugins
 
-JupyterLab can be extended in two ways: via top level application extensions
-or document widget extensions.  Application extensions extend the 
+JupyterLab can be extended in two ways: via top level application plugins
+or document widget extensions.  Application plugins extend the 
 functionality of JupyterLab itself and are the focus of this tutorial. 
 Document widget extensions extend the functionality of document widgets added 
 to the application and are covered in the Documents tutorial.
 
-The JupyterLab Application object is passed to all extensions and is 
-used to add content to the main area and the sidebars, as well as 
-add commands, keyboard shortcuts, and command palette entries.
+A JupyterLab application is comprised of Services and Extensions, as well as a 
+core [Application](https://github.com/phosphorjs/phosphide/blob/master/src/core/application.ts) object.
+
+## [Services](https://github.com/phosphorjs/phosphide/blob/master/src/core/serviceregistry.ts) 
+A service provider is used by extensions to add functionality to the
+application. 
+- Service providers can require other services.
+- Services are activated when they are needed by other services or extensions.
+- An example service is the [document registry](https://github.com/jupyter/jupyterlab/blob/master/src/docregistry/plugin.ts), which is used by extensions
+to add functionality around widgets backed by files.
 
 ## [Extensions](https://github.com/phosphorjs/phosphide/blob/master/src/core/extensionregistry.ts#L19) 
-Add content to the [application](https://github.com/phosphorjs/phosphide/blob/master/src/core/application.ts) itself or to services.
+Extensions use the Application object and optionally other services to provide 
+functionality to the application. 
+- Extensions provided to the application are activated immediately. 
 - An example extension is the [editor widget](https://github.com/jupyter/jupyterlab/blob/master/src/editorwidget/plugin.ts), which registers an 
 editor widget factory with the Document Registry.
 - Extensions are activated explicitly through the Application [instance](https://github.com/phosphorjs/phosphide/blob/master/src/core/application.ts#L71). 
-- The extensions provided to app on startup, are activated automatically
-
-## [Services](https://github.com/phosphorjs/phosphide/blob/master/src/core/serviceregistry.ts) 
-Provide functionality to other parts of the application.
-- An example service is the [document registry](https://github.com/jupyter/jupyterlab/blob/master/src/docregistry/plugin.ts), which is used by extensions
-to add functionality around widgets backed by files.
-- Services are activated on-demand.
 
 - A full example is contained [here](https://github.com/jupyter/jupyterlab/tree/master/examples/lab).