reactor-core/src/main/java/reactor/core/publisher/Mono.java
public final <R> Flux<R> flatMapIterable(Function<? super T, ? extends Iterable<? extends R>> mapper) {
		return Flux.onAssembly(new MonoFlattenIterable<>(this, mapper, Integer
				.MAX_VALUE, Queues.one()));
	}
public final <R> Flux<R> flatMapIterable(Function<? super T, ? extends Iterable<? extends R>> mapper) {
		return Flux.onAssembly(new MonoFlattenIterable<>(this, mapper, Integer
				.MAX_VALUE, Queues.one()));
	}
Transform the item emitted by this {@link Mono} into {@link Iterable}, then forward
its elements into the returned {@link Flux}. The prefetch argument allows to
give an arbitrary prefetch size to the inner {@link Iterable}.

<p>
<img class="marble" src="doc-files/marbles/flatMapIterableForMono.svg" alt="">

@param mapper the {@link Function} to transform input item into a sequence {@link Iterable}
@param <R> the merged output sequence type

@return a merged {@link Flux}