add repository draft

src/Umbraco.Web.UI.Client/.storybook/preview.js

@@ -103,12 +103,10 @@ export const parameters = {
 						'Sections',
 						'Section Views',
 						'Section Sidebar Items',
-						'Section Menus',
-						'Trees',
 						'Entity Actions',
 						'Workspaces',
-						'Workspace Actions',
 						'Property Editors',
+						'Repositories',
 						'*',
 					],
 					'*',

src/Umbraco.Web.UI.Client/src/stories/extending/repositories.mdx

@@ -0,0 +1,28 @@
+import { Meta } from '@storybook/addon-docs';
+
+<Meta title="Guides/Extending the Backoffice/Repositories" parameters={{ previewTabs: { canvas: { hidden: true } } }} />
+
+# Repositories
+
+TODO: make this understandable for others
+
+A repository is the Backoffices entry point to request data and get notified about updates. Each domain should register their own repository in the Backoffice.
+
+## Register a repository:
+
+TODO: add manifest
+
+With a repository we can have different data sources depending on the state of the app. It can be from a server, an offline database, a store, a Signal-R connection, etc. That means that the consumer will not have to be concerned how to access the data, add or remove items from a collection of items, etc. This means we get a loose connection between the consumer and the data storing procedures hiding all complex implementation.
+
+## Data flow with a repository
+
+TODO: add image of data flow
+
+A repository has to be instanced in the context where it is used. It should take a host element as part of the constructor, so any contexts consumed in the repository (notifications, modals, etc.) get rendered in the correct DOM context.
+
+A repository can be called directly from an element, but will often be instantiated in a context, like the Workspace Context.
+
+## The Repository Class
+
+TODO: get typescript interface
+TODO: show repository example: