/** Factory for constructing {@link FlatMapSpliterator} instances. */
    interface Factory<InElementT extends @Nullable Object, OutSpliteratorT extends Spliterator<?>> {
      OutSpliteratorT newFlatMapSpliterator(
          @Nullable OutSpliteratorT prefix,
          Spliterator<InElementT> fromSplit,
          Function<? super InElementT, @Nullable OutSpliteratorT> function,
          int splitCharacteristics,

    @IgnoreJRERequirement // should be redundant with the annotations on *both* enclosing classes
    interface Factory<InElementT extends @Nullable Object, OutSpliteratorT extends Spliterator<?>> {
      OutSpliteratorT newFlatMapSpliterator(
          @Nullable OutSpliteratorT prefix,
          Spliterator<InElementT> fromSplit,
          Function<? super InElementT, @Nullable OutSpliteratorT> function,
          int splitCharacteristics,