Improve `useMaterial3` documentation (#104815)

* Improve `useMaterial3` documentation

* reverse styles and components

* tweak language around support

* Update theme_data.dart

* remove trailing space

* Update packages/flutter/lib/src/material/theme_data.dart
Co-authored-by: Darren Austin <darren@darrenaustin.org>

* add missing spec links

* remove spec links from useMaterial3

* move defaults section up, rejig things

* spaces no longer trailing

* spaces no longer trailing (2)
Co-authored-by: Darren Austin <darren@darrenaustin.org>

packages/flutter/lib/src/material/app_bar.dart

@@ -152,6 +152,7 @@ class _PreferredAppBarSize extends Size {
 ///  * [FlexibleSpaceBar], which is used with [flexibleSpace] when the app bar
 ///    can expand and collapse.
 ///  * <https://material.io/design/components/app-bars-top.html>
+///  * <https://m3.material.io/components/top-app-bar>
 ///  * Cookbook: [Place a floating app bar above a list](https://flutter.dev/docs/cookbook/lists/floating-app-bar)
 class AppBar extends StatefulWidget implements PreferredSizeWidget {
   /// Creates a Material Design app bar.

packages/flutter/lib/src/material/bottom_navigation_bar.dart

@@ -123,6 +123,7 @@ enum BottomNavigationBarLandscapeLayout {
 ///  * [BottomNavigationBarItem]
 ///  * [Scaffold]
 ///  * <https://material.io/design/components/bottom-navigation.html>
+///  * [NavigationBar], this widget's replacement in Material Design 3.
 class BottomNavigationBar extends StatefulWidget {
   /// Creates a bottom navigation bar which is typically used as a
   /// [Scaffold]'s [Scaffold.bottomNavigationBar] argument.

packages/flutter/lib/src/material/card.dart

@@ -53,6 +53,7 @@ import 'theme.dart';
 ///  * [ListTile], to display icons and text in a card.
 ///  * [showDialog], to display a modal card.
 ///  * <https://material.io/design/components/cards.html>
+///  * <https://m3.material.io/components/cards>
 class Card extends StatelessWidget {
   /// Creates a Material Design card.
   ///

packages/flutter/lib/src/material/dialog.dart

@@ -169,10 +169,10 @@ class Dialog extends StatelessWidget {
 
 /// A Material Design alert dialog.
 ///
-/// An alert dialog informs the user about situations that require
-/// acknowledgement. An alert dialog has an optional title and an optional list
-/// of actions. The title is displayed above the content and the actions are
-/// displayed below the content.
+/// An alert dialog (also known as a basic dialog) informs the user about
+/// situations that require acknowledgement. An alert dialog has an optional
+/// title and an optional list of actions. The title is displayed above the
+/// content and the actions are displayed below the content.
 ///
 /// {@youtube 560 315 https://www.youtube.com/watch?v=75CsnyRXf5I}
 ///
@@ -251,6 +251,7 @@ class Dialog extends StatelessWidget {
 ///  * [CupertinoAlertDialog], an iOS-styled alert dialog.
 ///  * [showDialog], which actually displays the dialog and returns its result.
 ///  * <https://material.io/design/components/dialogs.html#alert-dialog>
+///  * <https://m3.material.io/components/dialogs>
 class AlertDialog extends StatelessWidget {
   /// Creates an alert dialog.
   ///
@@ -1060,6 +1061,7 @@ Widget _buildMaterialDialogTransitions(BuildContext context, Animation<double> a
 ///  * [DisplayFeatureSubScreen], which documents the specifics of how
 ///    [DisplayFeature]s can split the screen into sub-screens.
 ///  * <https://material.io/design/components/dialogs.html>
+///  * <https://m3.material.io/components/dialogs>
 Future<T?> showDialog<T>({
   required BuildContext context,
   required WidgetBuilder builder,

packages/flutter/lib/src/material/elevated_button.dart

@@ -57,6 +57,7 @@ import 'theme_data.dart';
 ///  * [TextButton], a simple flat button without a shadow.
 ///  * [OutlinedButton], a [TextButton] with a border outline.
 ///  * <https://material.io/design/components/buttons.html>
+///  * <https://m3.material.io/components/buttons>
 class ElevatedButton extends ButtonStyleButton {
   /// Create an ElevatedButton.
   ///

packages/flutter/lib/src/material/floating_action_button.dart

@@ -89,6 +89,7 @@ enum _FloatingActionButtonType {
 ///  * [Scaffold], in which floating action buttons typically live.
 ///  * [ElevatedButton], a filled button whose material elevates when pressed.
 ///  * <https://material.io/design/components/buttons-floating-action-button.html>
+///  * <https://m3.material.io/components/floating-action-button>
 class FloatingActionButton extends StatelessWidget {
   /// Creates a circular floating action button.
   ///
@@ -235,6 +236,9 @@ class FloatingActionButton extends StatelessWidget {
   /// The [label], [autofocus], and [clipBehavior] arguments must not be null.
   /// Additionally, [elevation], [highlightElevation], and [disabledElevation]
   /// (if specified) must be non-negative.
+  ///
+  /// See also:
+  ///  * <https://m3.material.io/components/extended-fab>
   const FloatingActionButton.extended({
     super.key,
     this.tooltip,

packages/flutter/lib/src/material/list_tile.dart

@@ -291,6 +291,7 @@ enum ListTileControlAffinity {
 ///  * <https://material.io/design/components/lists.html>
 ///  * Cookbook: [Use lists](https://flutter.dev/docs/cookbook/lists/basic-list)
 ///  * Cookbook: [Implement swipe to dismiss](https://flutter.dev/docs/cookbook/gestures/dismissible)
+// TODO(plg): Add link to m3 spec below m2 spec link when available
 class ListTile extends StatelessWidget {
   /// Creates a list tile.
   ///

packages/flutter/lib/src/material/material.dart

@@ -164,6 +164,7 @@ abstract class MaterialInkController {
 ///  * [MergeableMaterial], a piece of material that can split and re-merge.
 ///  * [Card], a wrapper for a [Material] of [type] [MaterialType.card].
 ///  * <https://material.io/design/>
+///  * <https://m3.material.io/styles/color/the-color-system/color-roles>
 class Material extends StatefulWidget {
   /// Creates a piece of material.
   ///

packages/flutter/lib/src/material/navigation_bar.dart

@@ -48,6 +48,7 @@ import 'tooltip.dart';
 ///  * [NavigationDestination]
 ///  * [BottomNavigationBar]
 ///  * <https://api.flutter.dev/flutter/material/NavigationDestination-class.html>
+///  * <https://m3.material.io/components/navigation-bar>
 class NavigationBar extends StatelessWidget {
   /// Creates a Material 3 Navigation Bar component.
   ///

packages/flutter/lib/src/material/navigation_rail.dart

@@ -61,7 +61,8 @@ import 'theme.dart';
 ///    destinations in the navigation rail.
 ///  * [BottomNavigationBar], which is a similar navigation widget that's laid
 ///     out horizontally.
-///  * https://material.io/components/navigation-rail/
+///  * <https://material.io/components/navigation-rail/>
+///  * <https://m3.material.io/components/navigation-rail>
 class NavigationRail extends StatefulWidget {
   /// Creates a Material Design navigation rail.
   ///

packages/flutter/lib/src/material/outlined_button.dart

@@ -62,6 +62,7 @@ import 'theme_data.dart';
 ///  * [ElevatedButton], a filled Material Design button with a shadow.
 ///  * [TextButton], a Material Design button without a shadow.
 ///  * <https://material.io/design/components/buttons.html>
+///  * <https://m3.material.io/components/buttons>
 class OutlinedButton extends ButtonStyleButton {
   /// Create an OutlinedButton.
   ///

packages/flutter/lib/src/material/text_button.dart

@@ -62,6 +62,7 @@ import 'theme_data.dart';
 ///  * [OutlinedButton], a [TextButton] with a border outline.
 ///  * [ElevatedButton], a filled button whose material elevates when pressed.
 ///  * <https://material.io/design/components/buttons.html>
+///  * <https://m3.material.io/components/buttons>
 class TextButton extends ButtonStyleButton {
   /// Create a TextButton.
   ///

packages/flutter/lib/src/material/theme_data.dart

@@ -1133,53 +1133,63 @@ class ThemeData with Diagnosticable {
 
   /// A temporary flag used to opt-in to Material 3 features.
   ///
-  /// If true, then components that have been migrated to Material 3 will
+  /// If true, then widgets that have been migrated to Material 3 will
   /// use new colors, typography and other features of Material 3.
   /// If false, they will use the Material 2 look and feel.
   ///
+  /// During the migration to Material 3, turning this on may yield
+  /// inconsistent look and feel in your app as some widgets are migrated
+  /// while others have yet to be.
+  ///
+  /// Defaults to false. When the Material 3 specification is complete
+  /// and all widgets are migrated on stable, we will change this flag to be
+  /// true by default. After that change has landed on stable, we will deprecate
+  /// this flag and remove all uses of it. At that point, the `material` library
+  /// will aim to only support Material 3.
+  ///
+  /// ## Defaults
   /// If a [ThemeData] is constructed with [useMaterial3] set to true, then
-  /// some properties will get special defaults. However, just copying a [ThemeData]
-  /// with [useMaterial3] set to true will not change any of these properties in the
-  /// resulting [ThemeData]. These properties are:
+  /// some properties will get updated defaults. Please note that
+  /// [ThemeData.copyWith] with [useMaterial3] set to true will
+  /// not change any of these properties in the resulting [ThemeData].
+  ///
   /// <style>table,td,th { border-collapse: collapse; padding: 0.45em; } td { border: 1px solid }</style>
   ///
-  /// | Property        | Material 3 default           | Fallback default          |
+  /// | Property        | Material 3 default           | Material 2 default        |
   /// | :-------------- | :--------------------------- | :------------------------ |
   /// | [typography]    | [Typography.material2021]    | [Typography.material2014] |
   /// | [splashFactory] | [InkSparkle]* or [InkRipple] | [InkSplash]               |
   ///
-  /// \* if and only if the target platform is Android and the app is not
+  /// \* if the target platform is Android and the app is not
   /// running on the web, otherwise it will fallback to [InkRipple].
   ///
-  /// During the migration to Material 3, turning this on may yield
-  /// inconsistent look and feel in your app. Some components will be migrated
-  /// before others and typography changes will be coming in stages.
-  ///
-  /// [useMaterial3] defaults to false. After all the migrated components
-  /// have landed on stable, we will change this to be true by default. After
-  /// that change has landed on stable, we will deprecate this flag and remove
-  /// all uses of it. Everything will use the Material 3 look and feel at
-  /// that point.
-  ///
-  /// Components that have been migrated to Material 3 are:
-  ///
-  ///   * [AlertDialog]
-  ///   * [AppBar]
-  ///   * [Card]
-  ///   * [Dialog]
-  ///   * [ElevatedButton]
-  ///   * [FloatingActionButton]
-  ///   * [Material]
-  ///   * [NavigationBar] (new, replacing [BottomNavigationBar])
-  ///   * [NavigationRail]
-  ///   * [OutlinedButton]
-  ///   * [StretchingOverscrollIndicator], replacing the
-  ///     [GlowingOverscrollIndicator]
-  ///   * [TextButton]
+  /// ## Affected widgets
+  ///
+  /// This flag affects styles and components.
+  ///
+  /// ### Styles
+  ///   * Color: [ColorScheme], [Material]
+  ///   * Shape: (see components below)
+  ///   * Typography: `typography` (see table above)
+  ///
+  /// ### Components
+  ///   * Common buttons: [TextButton], [OutlinedButton], [ElevatedButton]
+  ///   * FAB: [FloatingActionButton]
+  ///   * Extended FAB: [FloatingActionButton.extended]
+  ///   * Cards: [Card]
+  ///   * Dialogs: [Dialog], [AlertDialog]
+  ///   * Lists: [ListTile]
+  ///   * Navigation bar: [NavigationBar] (new, replacing [BottomNavigationBar])
+  ///   * [Navigation rail](https://m3.material.io/components/navigation-rail): [NavigationRail]
+  ///   * Top app bar: [AppBar]
+  ///
+  /// In addition, this flag enables features introduced in Android 12.
+  ///   * Stretch overscroll: [MaterialScrollBehavior]
+  ///   * Ripple: `splashFactory` (see table above)
   ///
   /// See also:
   ///
-  ///   * [Material Design 3](https://m3.material.io/).
+  ///   * [Material 3 specification](https://m3.material.io/).
   final bool useMaterial3;
 
   /// The density value for specifying the compactness of various UI components.

packages/flutter/lib/src/material/typography.dart

@@ -77,6 +77,7 @@ enum ScriptCategory {
 /// See also:
 ///
 ///  * <https://material.io/design/typography/>
+///  * <https://m3.material.io/styles/typography>
 @immutable
 class Typography with Diagnosticable {
   /// Creates a typography instance.
@@ -157,6 +158,9 @@ class Typography with Diagnosticable {
   ///
   /// The default values for [englishLike], [dense], and [tall] are
   /// [englishLike2021], [dense2021], and [tall2021].
+  ///
+  /// See also:
+  ///  * <https://m3.material.io/styles/typography>
   factory Typography.material2021({
     TargetPlatform? platform = TargetPlatform.android,
     TextTheme? black,