[3.41] Document content-based resizing for add-to-app on iOS

src/content/add-to-app/ios/add-flutter-screen.md

@@ -766,6 +766,70 @@ you're free to push data or prepare your Flutter environment
 in any way you'd like, before presenting the Flutter UI using a
 `FlutterViewController`.
 
+## Content-sized views
+
+On iOS, you can also set your embedded `FlutterView` to size itself based off its content.
+
+<Tabs key="darwin-language">
+<Tab name="Swift">
+
+```swift
+let flutterViewController = FlutterViewController(engine: engine, nibName: nil, bundle: nil)
+flutterViewController.isAutoResizable = true
+```
+
+</Tab>
+<Tab name="Objective-C">
+
+```objc
+_flutterViewController = [[FlutterViewController alloc] initWithEngine:engine nibName:nil bundle:nil];
+_flutterViewController.autoResizable = true;
+```
+
+</Tab>
+</Tabs>
+
+### Restrictions
+
+Since content-sized Flutter views require your Flutter app to be able to size itself,
+some widgets are not supported.
+
+* Widgets with unbounded size, like a `ListView`.
+* Widgets that defer to its child for the size, like `LayoutBuilder`.
+
+In practice, this means that quite a few common widgets are not supported,
+such as `ScaffoldBuilder`, `CupertinoTimerPicker`,
+or any widget that internally relies on a `LayoutBuilder`.
+When in doubt, you can use an `UnconstrainedBox` to test the usability of 
+a widget for a content-sized view, as in the following example:
+
+```dart
+import 'package:flutter/material.dart';
+
+void main() => runApp(MyApp());
+
+class MyApp extends StatelessWidget {
+  @override
+  Widget build(BuildContext context)
+  => MaterialApp(home: MyPage());
+}
+
+class MyPage extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+        body: UnconstrainedBox(
+          // TODO: Edit this line to check if a widget
+          // can cause problems with content-sized views.
+          child: Text('This works!'),
+          // child: Column(children: [Column(children: [Expanded(child: Text('This blows up!'))])]),
+          // child: ListView(children: [Text('This blows up!')]),
+        )
+    );
+  }
+}
+```
+For a working example, refer to this [sample project][].
 
 [`FlutterEngine`]: {{site.api}}/ios-embedder/interface_flutter_engine.html
 [`FlutterViewController`]: {{site.api}}/ios-embedder/interface_flutter_view_controller.html
@@ -785,6 +849,7 @@ in any way you'd like, before presenting the Flutter UI using a
 [`WidgetsApp`]: {{site.api}}/flutter/widgets/WidgetsApp-class.html
 [`PlatformDispatcher.defaultRouteName`]: {{site.api}}/flutter/dart-ui/PlatformDispatcher/defaultRouteName.html
 [Start a FlutterEngine and FlutterViewController section]:/add-to-app/ios/add-flutter-screen/#start-a-flutterengine-and-flutterviewcontroller
-[`Observable`]: https://developer.apple.com/documentation/observation/observable
-[`NavigationLink`]: https://developer.apple.com/documentation/swiftui/navigationlink
-[`Observable()`]: https://developer.apple.com/documentation/observation/observable()
+[`Observable`]: {{site.apple-dev}}/documentation/observation/observable
+[`NavigationLink`]: {{site.apple-dev}}/documentation/swiftui/navigationlink
+[`Observable()`]: {{site.apple-dev}}/documentation/observation/observable()
+[sample project]: {{site.repo.samples}}/tree/main/add_to_app/ios_content_resizing