add docs

packages/svelte/src/internal/client/proxy.js

@@ -48,7 +48,6 @@ export function proxy(value, immutable = true, owners) {
 
 		const prototype = get_prototype_of(value);
 
-		// TODO handle Map and Set as well
 		if (prototype === object_prototype || prototype === array_prototype) {
 			const proxy = new Proxy(value, state_proxy_handler);
 

sites/svelte-5-preview/src/routes/docs/content/01-api/02-runes.md

@@ -93,6 +93,25 @@ This can improve performance with large arrays and objects that you weren't plan
 
 > Objects and arrays passed to `$state.frozen` will be shallowly frozen using `Object.freeze()`. If you don't want this, pass in a clone of the object or array instead.
 
+### Reactive Map, Set and Date
+
+Svelte provides reactive wrappers for the native `Map`, `Set` and `Date` objects. These can be found imported from `svelte/reactivity` and used just like their native equivalents.
+
+```svelte
+<script>
+  import { Map } from 'svelte/reactivity';
+
+  const map = new Map();
+  map.set('message', 'hello');
+
+  function update_message() {
+    map.set('message', 'goodbye');
+  }
+</script>
+
+<p>{map.get('message')}</p>
+```
+
 ## `$derived`
 
 Derived state is declared with the `$derived` rune: