reactor-core/src/main/java/reactor/core/publisher/Flux.java
public static <I> Flux<I> mergeSequentialDelayError(Iterable<? extends Publisher<? extends I>> sources,
			int maxConcurrency, int prefetch) {
		return mergeSequential(sources, true, maxConcurrency, prefetch);
	}
public static <I> Flux<I> mergeSequentialDelayError(Iterable<? extends Publisher<? extends I>> sources,
			int maxConcurrency, int prefetch) {
		return mergeSequential(sources, true, maxConcurrency, prefetch);
	}
Merge data from {@link Publisher} sequences provided in an {@link Iterable}
into an ordered merged sequence. Unlike concat, sources are subscribed to
eagerly (but at most {@code maxConcurrency} sources at a time). Unlike merge, their
emitted values are merged into the final sequence in subscription order.
This variant will delay any error until after the rest of the mergeSequential backlog
has been processed.
<p>
<img class="marble" src="doc-files/marbles/mergeSequentialVarSources.svg" alt="">

@param sources an {@link Iterable} of {@link Publisher} sequences to merge
@param maxConcurrency the request produced to the main source thus limiting concurrent merge backlog
@param prefetch the inner source request size
@param <I> the merged type

@return a merged {@link Flux}, subscribing early but keeping the original ordering