diff --git a/packages/flutter/lib/src/services/text_editing.dart b/packages/flutter/lib/src/services/text_editing.dart
index 403fae5..8286540 100644
--- a/packages/flutter/lib/src/services/text_editing.dart
+++ b/packages/flutter/lib/src/services/text_editing.dart
@@ -238,8 +238,8 @@
   /// [TextSelection.extentOffset] to the given [TextPosition].
   ///
   /// In some cases, the [TextSelection.baseOffset] and
-  /// [TextSelection.extentOffset] may flip during this operation, or the size
-  /// of the selection may shrink.
+  /// [TextSelection.extentOffset] may flip during this operation, and/or the
+  /// size of the selection may shrink.
   ///
   /// ## Difference with [expandTo]
   /// In contrast with this method, [expandTo] is strictly growth; the
diff --git a/packages/flutter/lib/src/widgets/default_text_editing_shortcuts.dart b/packages/flutter/lib/src/widgets/default_text_editing_shortcuts.dart
index 8414590..370dd4b 100644
--- a/packages/flutter/lib/src/widgets/default_text_editing_shortcuts.dart
+++ b/packages/flutter/lib/src/widgets/default_text_editing_shortcuts.dart
@@ -307,8 +307,8 @@
     const SingleActivator(LogicalKeyboardKey.arrowUp, meta: true): const ExtendSelectionToDocumentBoundaryIntent(forward: false, collapseSelection: true),
     const SingleActivator(LogicalKeyboardKey.arrowDown, meta: true): const ExtendSelectionToDocumentBoundaryIntent(forward: true, collapseSelection: true),
 
-    const SingleActivator(LogicalKeyboardKey.arrowLeft, shift: true, meta: true): const ExtendSelectionToLineBreakIntent(forward: false, collapseSelection: false),
-    const SingleActivator(LogicalKeyboardKey.arrowRight, shift: true, meta: true): const ExtendSelectionToLineBreakIntent(forward: true, collapseSelection: false),
+    const SingleActivator(LogicalKeyboardKey.arrowLeft, shift: true, meta: true): const ExpandSelectionToLineBreakIntent(forward: false),
+    const SingleActivator(LogicalKeyboardKey.arrowRight, shift: true, meta: true): const ExpandSelectionToLineBreakIntent(forward: true),
     const SingleActivator(LogicalKeyboardKey.arrowUp, shift: true, meta: true): const ExtendSelectionToDocumentBoundaryIntent(forward: false, collapseSelection: false),
     const SingleActivator(LogicalKeyboardKey.arrowDown, shift: true, meta: true): const ExtendSelectionToDocumentBoundaryIntent(forward: true, collapseSelection: false),
 
diff --git a/packages/flutter/lib/src/widgets/editable_text.dart b/packages/flutter/lib/src/widgets/editable_text.dart
index 67f5674..9a09c50 100644
--- a/packages/flutter/lib/src/widgets/editable_text.dart
+++ b/packages/flutter/lib/src/widgets/editable_text.dart
@@ -2931,6 +2931,30 @@
 
   late final _UpdateTextSelectionToAdjacentLineAction<ExtendSelectionVerticallyToAdjacentLineIntent> _adjacentLineAction = _UpdateTextSelectionToAdjacentLineAction<ExtendSelectionVerticallyToAdjacentLineIntent>(this);
 
+  void _expandSelection(ExpandSelectionToLineBreakIntent intent) {
+    final _TextBoundary textBoundary = _linebreak(intent);
+    final TextSelection textBoundarySelection = textBoundary.textEditingValue.selection;
+    if (!textBoundarySelection.isValid) {
+      return;
+    }
+
+    final bool inOrder = textBoundarySelection.baseOffset <= textBoundarySelection.extentOffset;
+    final bool towardsExtent = intent.forward == inOrder;
+    final TextPosition position = towardsExtent
+        ? textBoundarySelection.extent
+        : textBoundarySelection.base;
+
+    final TextPosition newExtent = intent.forward
+      ? textBoundary.getTrailingTextBoundaryAt(position)
+      : textBoundary.getLeadingTextBoundaryAt(position);
+
+    final TextSelection newSelection = textBoundarySelection.expandTo(newExtent, textBoundarySelection.isCollapsed);
+    userUpdateTextEditingValue(
+      _value.copyWith(selection: newSelection),
+      SelectionChangedCause.keyboard,
+    );
+  }
+
   late final Map<Type, Action<Intent>> _actions = <Type, Action<Intent>>{
     DoNothingAndStopPropagationTextIntent: DoNothingAction(consumesKey: false),
     ReplaceTextIntent: _replaceTextAction,
@@ -2946,6 +2970,7 @@
     ExtendSelectionByCharacterIntent: _makeOverridable(_UpdateTextSelectionAction<ExtendSelectionByCharacterIntent>(this, false, _characterBoundary,)),
     ExtendSelectionToNextWordBoundaryIntent: _makeOverridable(_UpdateTextSelectionAction<ExtendSelectionToNextWordBoundaryIntent>(this, true, _nextWordBoundary)),
     ExtendSelectionToLineBreakIntent: _makeOverridable(_UpdateTextSelectionAction<ExtendSelectionToLineBreakIntent>(this, true, _linebreak)),
+    ExpandSelectionToLineBreakIntent: _makeOverridable(CallbackAction<ExpandSelectionToLineBreakIntent>(onInvoke: _expandSelection)),
     ExtendSelectionVerticallyToAdjacentLineIntent: _makeOverridable(_adjacentLineAction),
     ExtendSelectionToDocumentBoundaryIntent: _makeOverridable(_UpdateTextSelectionAction<ExtendSelectionToDocumentBoundaryIntent>(this, true, _documentBoundary)),
     ExtendSelectionToNextWordBoundaryOrCaretLocationIntent: _makeOverridable(_ExtendSelectionOrCaretPositionAction(this, _nextWordBoundary)),
diff --git a/packages/flutter/lib/src/widgets/text_editing_intents.dart b/packages/flutter/lib/src/widgets/text_editing_intents.dart
index f75ad6e..b4554f5 100644
--- a/packages/flutter/lib/src/widgets/text_editing_intents.dart
+++ b/packages/flutter/lib/src/widgets/text_editing_intents.dart
@@ -92,7 +92,7 @@
   final bool collapseAtReversal;
 }
 
-/// Expands, or moves the current selection from the current
+/// Extends, or moves the current selection from the current
 /// [TextSelection.extent] position to the previous or the next character
 /// boundary.
 class ExtendSelectionByCharacterIntent extends DirectionalCaretMovementIntent {
@@ -103,7 +103,7 @@
   }) : super(forward, collapseSelection);
 }
 
-/// Expands, or moves the current selection from the current
+/// Extends, or moves the current selection from the current
 /// [TextSelection.extent] position to the previous or the next word
 /// boundary.
 class ExtendSelectionToNextWordBoundaryIntent extends DirectionalCaretMovementIntent {
@@ -114,7 +114,7 @@
   }) : super(forward, collapseSelection);
 }
 
-/// Expands, or moves the current selection from the current
+/// Extends, or moves the current selection from the current
 /// [TextSelection.extent] position to the previous or the next word
 /// boundary, or the [TextSelection.base] position if it's closer in the move
 /// direction.
@@ -124,7 +124,7 @@
 /// when the order of [TextSelection.base] and [TextSelection.extent] would
 /// reverse.
 ///
-/// This is typically only used on macOS.
+/// This is typically only used on MacOS.
 class ExtendSelectionToNextWordBoundaryOrCaretLocationIntent extends DirectionalTextEditingIntent {
   /// Creates an [ExtendSelectionToNextWordBoundaryOrCaretLocationIntent].
   const ExtendSelectionToNextWordBoundaryOrCaretLocationIntent({
@@ -132,9 +132,33 @@
   }) : super(forward);
 }
 
-/// Expands, or moves the current selection from the current
+/// Expands the current selection to the closest line break in the direction
+/// given by [forward].
+///
+/// Either the base or extent can move, whichever is closer to the line break.
+/// The selection will never shrink.
+///
+/// This behavior is common on MacOS.
+///
+/// See also:
+///
+///   [ExtendSelectionToLineBreakIntent], which is similar but always moves the
+///   extent.
+class ExpandSelectionToLineBreakIntent extends DirectionalTextEditingIntent {
+  /// Creates an [ExpandSelectionToLineBreakIntent].
+  const ExpandSelectionToLineBreakIntent({
+    required bool forward,
+  }) : super(forward);
+}
+
+/// Extends, or moves the current selection from the current
 /// [TextSelection.extent] position to the closest line break in the direction
 /// given by [forward].
+///
+/// See also:
+///
+///   [ExpandSelectionToLineBreakIntent], which is similar but always increases
+///   the size of the selection.
 class ExtendSelectionToLineBreakIntent extends DirectionalCaretMovementIntent {
   /// Creates an [ExtendSelectionToLineBreakIntent].
   const ExtendSelectionToLineBreakIntent({
@@ -145,7 +169,7 @@
        super(forward, collapseSelection, collapseAtReversal);
 }
 
-/// Expands, or moves the current selection from the current
+/// Extends, or moves the current selection from the current
 /// [TextSelection.extent] position to the closest position on the adjacent
 /// line.
 class ExtendSelectionVerticallyToAdjacentLineIntent extends DirectionalCaretMovementIntent {
@@ -156,7 +180,7 @@
   }) : super(forward, collapseSelection);
 }
 
-/// Expands, or moves the current selection from the current
+/// Extends, or moves the current selection from the current
 /// [TextSelection.extent] position to the start or the end of the document.
 class ExtendSelectionToDocumentBoundaryIntent extends DirectionalCaretMovementIntent {
   /// Creates an [ExtendSelectionToDocumentBoundaryIntent].
diff --git a/packages/flutter/test/widgets/editable_text_test.dart b/packages/flutter/test/widgets/editable_text_test.dart
index d94fd00..74a9384 100644
--- a/packages/flutter/test/widgets/editable_text_test.dart
+++ b/packages/flutter/test/widgets/editable_text_test.dart
@@ -4682,17 +4682,41 @@
       targetPlatform: defaultTargetPlatform,
     );
 
-    expect(
-      selection,
-      equals(
-        const TextSelection(
-          baseOffset: 20,
-          extentOffset: 36,
-          affinity: TextAffinity.upstream,
-        ),
-      ),
-      reason: 'on $platform',
-    );
+    switch (defaultTargetPlatform) {
+      // These platforms extend by line.
+      case TargetPlatform.iOS:
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+      case TargetPlatform.linux:
+      case TargetPlatform.windows:
+        expect(
+          selection,
+          equals(
+            const TextSelection(
+              baseOffset: 20,
+              extentOffset: 36,
+              affinity: TextAffinity.upstream,
+            ),
+          ),
+          reason: 'on $platform',
+        );
+        break;
+
+      // Mac expands by line.
+      case TargetPlatform.macOS:
+        expect(
+          selection,
+          equals(
+            const TextSelection(
+              baseOffset: 20,
+              extentOffset: 54,
+              affinity: TextAffinity.upstream,
+            ),
+          ),
+          reason: 'on $platform',
+        );
+        break;
+    }
 
     // Select All
     await sendKeys(
@@ -8502,7 +8526,7 @@
     expect(controller.selection.baseOffset, 17);
     expect(controller.selection.extentOffset, 24);
 
-    // Multiple expandLeftByLine shortcuts only move ot the start of the line
+    // Multiple expandLeftByLine shortcuts only move to the start of the line
     // and not to the previous line.
     await sendKeys(
       tester,
@@ -8516,8 +8540,23 @@
       targetPlatform: defaultTargetPlatform,
     );
     expect(controller.selection.isCollapsed, false);
-    expect(controller.selection.baseOffset, 17);
-    expect(controller.selection.extentOffset, 15);
+    switch (defaultTargetPlatform) {
+      // These platforms extend by line.
+      case TargetPlatform.iOS:
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+      case TargetPlatform.linux:
+      case TargetPlatform.windows:
+        expect(controller.selection.baseOffset, 17);
+        expect(controller.selection.extentOffset, 15);
+        break;
+
+      // Mac expands by line.
+      case TargetPlatform.macOS:
+        expect(controller.selection.baseOffset, 15);
+        expect(controller.selection.extentOffset, 24);
+        break;
+    }
 
     // Set the caret to the end of a line.
     controller.selection = const TextSelection(
@@ -8599,6 +8638,343 @@
     // On web, using keyboard for selection is handled by the browser.
   }, variant: TargetPlatformVariant.all(), skip: kIsWeb); // [intended]
 
+  testWidgets("Mac's expand by line behavior on multiple lines", (WidgetTester tester) async {
+    const String multilineText = 'word word word\nword word\nword'; // 15 + 10 + 4;
+    final TextEditingController controller = TextEditingController(text: multilineText);
+    // word word word
+    // wo|rd word
+    // w|ord
+    controller.selection = const TextSelection(
+      baseOffset: 17,
+      extentOffset: 26,
+      affinity: TextAffinity.upstream,
+    );
+    await tester.pumpWidget(MaterialApp(
+      home: Align(
+        alignment: Alignment.topLeft,
+        child: SizedBox(
+          width: 400,
+          child: EditableText(
+            maxLines: 10,
+            controller: controller,
+            autofocus: true,
+            focusNode: focusNode,
+            style: Typography.material2018().black.subtitle1!,
+            cursorColor: Colors.blue,
+            backgroundCursorColor: Colors.grey,
+            keyboardType: TextInputType.text,
+          ),
+        ),
+      ),
+    ));
+
+    await tester.pump(); // Wait for autofocus to take effect.
+    expect(controller.selection.isCollapsed, false);
+    expect(controller.selection.baseOffset, 17);
+    expect(controller.selection.extentOffset, 26);
+
+    // Expanding right to the end of the line moves the extent on the second
+    // selected line.
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowRight,
+      ],
+      shift: true,
+      lineModifier: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    expect(controller.selection.isCollapsed, false);
+    expect(controller.selection.baseOffset, 17);
+    expect(controller.selection.extentOffset, 29);
+
+    // Expanding right again does nothing.
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowRight,
+        LogicalKeyboardKey.arrowRight,
+        LogicalKeyboardKey.arrowRight,
+      ],
+      shift: true,
+      lineModifier: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    expect(controller.selection.isCollapsed, false);
+    expect(controller.selection.baseOffset, 17);
+    expect(controller.selection.extentOffset, 29);
+
+    // Expanding left by line moves the base on the first selected line to the
+    // beginning of that line.
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowLeft,
+      ],
+      shift: true,
+      lineModifier: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    expect(controller.selection.isCollapsed, false);
+    expect(controller.selection.baseOffset, 15);
+    expect(controller.selection.extentOffset, 29);
+
+    // Expanding left again does nothing.
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowLeft,
+        LogicalKeyboardKey.arrowLeft,
+        LogicalKeyboardKey.arrowLeft,
+      ],
+      shift: true,
+      lineModifier: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    expect(controller.selection.isCollapsed, false);
+    expect(controller.selection.baseOffset, 15);
+    expect(controller.selection.extentOffset, 29);
+  },
+    // On web, using keyboard for selection is handled by the browser.
+    skip: kIsWeb, // [intended]
+    variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.macOS })
+  );
+
+  testWidgets("Mac's expand extent position", (WidgetTester tester) async {
+    const String testText = 'Now is the time for all good people to come to the aid of their country';
+    final TextEditingController controller = TextEditingController(text: testText);
+    // Start the selection in the middle somewhere.
+    controller.selection = const TextSelection.collapsed(offset: 10);
+    await tester.pumpWidget(MaterialApp(
+      home: Align(
+        alignment: Alignment.topLeft,
+        child: SizedBox(
+          width: 400,
+          child: EditableText(
+            maxLines: 10,
+            controller: controller,
+            autofocus: true,
+            focusNode: focusNode,
+            style: Typography.material2018().black.subtitle1!,
+            cursorColor: Colors.blue,
+            backgroundCursorColor: Colors.grey,
+            keyboardType: TextInputType.text,
+          ),
+        ),
+      ),
+    ));
+
+    await tester.pump(); // Wait for autofocus to take effect.
+    expect(controller.selection.isCollapsed, true);
+    expect(controller.selection.baseOffset, 10);
+
+    // With cursor in the middle of the line, cmd + left. Left end is the extent.
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowLeft,
+      ],
+      lineModifier: true,
+      shift: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    expect(
+      controller.selection,
+      equals(
+        const TextSelection(
+          baseOffset: 10,
+          extentOffset: 0,
+          affinity: TextAffinity.upstream,
+        ),
+      ),
+    );
+
+    // With cursor in the middle of the line, cmd + right. Right end is the extent.
+    controller.selection = const TextSelection.collapsed(offset: 10);
+    await tester.pump();
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowRight,
+      ],
+      lineModifier: true,
+      shift: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    expect(
+      controller.selection,
+      equals(
+        const TextSelection(
+          baseOffset: 10,
+          extentOffset: 29,
+          affinity: TextAffinity.upstream,
+        ),
+      ),
+    );
+
+    // With cursor in the middle of the line, cmd + left then cmd + right. Left end is the extent.
+    controller.selection = const TextSelection.collapsed(offset: 10);
+    await tester.pump();
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowLeft,
+      ],
+      lineModifier: true,
+      shift: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    await tester.pump();
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowRight,
+      ],
+      lineModifier: true,
+      shift: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    expect(
+      controller.selection,
+      equals(
+        const TextSelection(
+          baseOffset: 29,
+          extentOffset: 0,
+          affinity: TextAffinity.upstream,
+        ),
+      ),
+    );
+
+    // With cursor in the middle of the line, cmd + right then cmd + left. Right end is the extent.
+    controller.selection = const TextSelection.collapsed(offset: 10);
+    await tester.pump();
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowRight,
+      ],
+      lineModifier: true,
+      shift: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    await tester.pump();
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowLeft,
+      ],
+      lineModifier: true,
+      shift: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    expect(
+      controller.selection,
+      equals(
+        const TextSelection(
+          baseOffset: 0,
+          extentOffset: 29,
+          affinity: TextAffinity.upstream,
+        ),
+      ),
+    );
+
+    // With an RTL selection in the middle of the line, cmd + left. Left end is the extent.
+    controller.selection = const TextSelection(baseOffset: 12, extentOffset: 8);
+    await tester.pump();
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowLeft,
+      ],
+      lineModifier: true,
+      shift: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    expect(
+      controller.selection,
+      equals(
+        const TextSelection(
+          baseOffset: 12,
+          extentOffset: 0,
+          affinity: TextAffinity.upstream,
+        ),
+      ),
+    );
+
+    // With an RTL selection in the middle of the line, cmd + right. Left end is the extent.
+    controller.selection = const TextSelection(baseOffset: 12, extentOffset: 8);
+    await tester.pump();
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowRight,
+      ],
+      lineModifier: true,
+      shift: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    expect(
+      controller.selection,
+      equals(
+        const TextSelection(
+          baseOffset: 29,
+          extentOffset: 8,
+          affinity: TextAffinity.upstream,
+        ),
+      ),
+    );
+
+    // With an LTR selection in the middle of the line, cmd + right. Right end is the extent.
+    controller.selection = const TextSelection(baseOffset: 8, extentOffset: 12);
+    await tester.pump();
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowRight,
+      ],
+      lineModifier: true,
+      shift: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    expect(
+      controller.selection,
+      equals(
+        const TextSelection(
+          baseOffset: 8,
+          extentOffset: 29,
+          affinity: TextAffinity.upstream,
+        ),
+      ),
+    );
+
+    // With an LTR selection in the middle of the line, cmd + left. Right end is the extent.
+    controller.selection = const TextSelection(baseOffset: 8, extentOffset: 12);
+    await tester.pump();
+    await sendKeys(
+      tester,
+      <LogicalKeyboardKey>[
+        LogicalKeyboardKey.arrowLeft,
+      ],
+      lineModifier: true,
+      shift: true,
+      targetPlatform: defaultTargetPlatform,
+    );
+    expect(
+      controller.selection,
+      equals(
+        const TextSelection(
+          baseOffset: 0,
+          extentOffset: 12,
+          affinity: TextAffinity.upstream,
+        ),
+      ),
+    );
+  },
+    // On web, using keyboard for selection is handled by the browser.
+    skip: kIsWeb, // [intended]
+    variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.macOS })
+  );
+
   testWidgets('expanding selection to start/end', (WidgetTester tester) async {
     final TextEditingController controller = TextEditingController(text: 'word word word');
     // word wo|rd| word