code: public final Flux<T> timeout(Duration timeout, @Nullable Publisher<? extends T> fallback) {
  		return timeout(timeout, fallback, Schedulers.parallel());
  	}
docs: Switch to a fallback {@link Flux} as soon as no item is emitted within the
  given {@link Duration} from the previous emission (or the subscription for the first item).
  <p>
  If the given {@link Publisher} is null, signal a {@link TimeoutException} instead.
  
  <p>
  <img class="marble" src="doc-files/marbles/timeoutFallbackForFlux.svg" alt="">
  
  @param timeout the timeout between two signals from this {@link Flux}
  @param fallback the fallback {@link Publisher} to subscribe when a timeout occurs
  
  @return a {@link Flux} that will fallback to a different {@link Publisher} in case of a per-item timeout