Add docs for LocalAutosaveMonitor and __experimentalUpdateLocalAutosa…

…veInterval (#19915)

packages/edit-post/src/store/actions.js

@@ -196,6 +196,13 @@ export function updatePreferredStyleVariations( blockName, blockStyle ) {
 	};
 }
 
+/**
+ * Returns an action object used in signalling that the editor should attempt
+ * to locally autosave the current post every `interval` seconds.
+ *
+ * @param {number} interval The new interval, in seconds.
+ * @return {Object} Action object.
+ */
 export function __experimentalUpdateLocalAutosaveInterval( interval ) {
 	return {
 		type: 'UPDATE_LOCAL_AUTOSAVE_INTERVAL',

packages/editor/src/components/local-autosave-monitor/README.md

@@ -0,0 +1,20 @@
+# LocalAutosaveMonitor
+
+`LocalAutosaveMonitor` is a component based on `AutosaveMonitor` that ensures that a local copy of the current post is regularly saved in `sessionStorage`. Additionally, it will:
+
+- attempt to clear the local copy if a copy is successful saved on the server;
+- warn the user upon loading a post that there is a local copy that can be loaded;
+- defer to remote autosaves, if any is available.
+
+`LocalAutosaveMonitor` observes a saving interval defined specifically for local autosaves, in contrast with remote (server-side) autosaving. See editor setting `__experimentalLocalAutosaveInterval` and setter `__experimentalUpdateLocalAutosaveInterval`.
+
+## Example
+
+```js
+const MyLayout = () => (
+	<main>
+		<LocalAutosaveMonitor />
+		<MyEditor />
+	</main>
+);
+```