Address comments.

packages/application-extension/src/index.tsx

@@ -749,7 +749,8 @@ const paths: JupyterFrontEndPlugin<JupyterFrontEnd.IPaths> = {
 };
 
 /**
- * The default JupyterLab paths dictionary provider.
+ * The default JupyterLab connection lost provider. This may be overridden
+ * to provide custom behavior when a connection to the server is lost.
  */
 const connectionlost: JupyterFrontEndPlugin<IConnectionLost> = {
   id: '@jupyterlab/apputils-extension:connectionlost',

packages/application/src/connectionlost.ts

@@ -7,6 +7,9 @@ import { ServerConnection, ServiceManager } from '@jupyterlab/services';
 
 import { IConnectionLost } from './tokens';
 
+/**
+ * A default connection lost handler, which brings up an error dialog.
+ */
 export const ConnectionLost: IConnectionLost = async function(
   manager: ServiceManager.IManager,
   err: ServerConnection.NetworkError