diff --git a/packages/flutter/lib/src/material/tab_controller.dart b/packages/flutter/lib/src/material/tab_controller.dart
index 986cfc3..e91a4fd 100644
--- a/packages/flutter/lib/src/material/tab_controller.dart
+++ b/packages/flutter/lib/src/material/tab_controller.dart
@@ -150,7 +150,12 @@
   int get previousIndex => _previousIndex;
   int _previousIndex;
 
-  /// True while we're animating from [previousIndex] to [index].
+  /// True while we're animating from [previousIndex] to [index] as a
+  /// consequence of calling [animateTo].
+  ///
+  /// This value is true during the [animateTo] animation that's triggered when
+  /// the user taps a [TabBar] tab. It is false when [offset] is changing as a
+  /// consequence of the user dragging (and "flinging") the [TabBarView].
   bool get indexIsChanging => _indexIsChangingCount != 0;
   int _indexIsChangingCount = 0;