anchor.diff:  ///   without invoking the overridden method.
   const _MustCallSuper mustCallSuper = const _MustCallSuper();
   
  -/// Used to annotate a class declaration `C`. Indicates that any type arguments
  -/// declared on `C` are to be treated as optional.  Tools such as the analyzer
  -/// and linter can use this information to suppress warnings that would
  -/// otherwise require type arguments to be provided for instances of `C`.
  +/// Used to annotate a class, mixin, or extension declaration `C`. Indicates
  +/// that any type arguments declared on `C` are to be treated as optional.
  +/// Tools such as the analyzer and linter can use this information to suppress
  +/// warnings that would otherwise require type arguments on `C` to be provided.
   const _OptionalTypeArgs optionalTypeArgs = const _OptionalTypeArgs();
   
   /// Used to annotate an instance member (method, getter, setter, operator, or
  
positive.code: /// Tools, such as the analyzer, can provide feedback if
  ///
  /// * the annotation is associated with a declaration other than a public
  ///   instance member in a class, or
  /// * the member is referenced outside of the defining library.
  const _VisibleForOverriding visibleForOverriding =
      const _VisibleForOverriding();
  
negative.code: /// Tools, such as the analyzer, can provide feedback if
  ///
  /// * the annotation is associated with a declaration not in the `lib` folder
  ///   of a package, or a private declaration, or a declaration in an unnamed
  ///   static extension, or
  /// * the declaration is referenced outside of its the defining library or a
  ///   library which is in the `test` folder of the defining package.
  const _VisibleForTesting visibleForTesting = const _VisibleForTesting();
  