code: public final Mono<T> timeout(Duration timeout, Mono<? extends T> fallback) {
  		return timeout(timeout, fallback, Schedulers.parallel());
  	}
docs: Switch to a fallback {@link Mono} in case no item arrives within the given {@link Duration}.
  
  <p>
  If the fallback {@link Mono} is null, signal a {@link TimeoutException} instead.
  
  <p>
  <img class="marble" src="doc-files/marbles/timeoutFallbackForMono.svg" alt="">
  
  @param timeout the timeout before the onNext signal from this {@link Mono}
  @param fallback the fallback {@link Mono} to subscribe to when a timeout occurs
  
  @return a {@link Mono} that will fallback to a different {@link Mono} in case of timeout