Update doc header in Opacity class to fix issue #23311 (#23475)
diff --git a/packages/flutter/lib/src/widgets/basic.dart b/packages/flutter/lib/src/widgets/basic.dart
index 12410f3..0f85966 100644
--- a/packages/flutter/lib/src/widgets/basic.dart
+++ b/packages/flutter/lib/src/widgets/basic.dart
@@ -143,7 +143,7 @@
/// This is more efficient than adding and removing the child widget from the
/// tree on demand.
///
-/// ## Opacity animation
+/// ## Performance considerations for opacity animation
///
/// Animating an [Opacity] widget directly causes the widget (and possibly its
/// subtree) to rebuild each frame, which is not very efficient. Consider using
