src/main/java/io/reactivex/Flowable.java
@SuppressWarnings({ "unchecked", "rawtypes" })
    @CheckReturnValue
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Flowable<T> concatDelayError(Publisher<? extends Publisher<? extends T>> sources, int prefetch, boolean tillTheEnd) {
        return fromPublisher(sources).concatMapDelayError((Function)Functions.identity(), prefetch, tillTheEnd);
    }
@SuppressWarnings({ "unchecked", "rawtypes" })
    @CheckReturnValue
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Flowable<T> concatDelayError(Publisher<? extends Publisher<? extends T>> sources, int prefetch, boolean tillTheEnd) {
        return fromPublisher(sources).concatMapDelayError((Function)Functions.identity(), prefetch, tillTheEnd);
    }
Concatenates the Publisher sequence of Publishers into a single sequence by subscribing to each inner Publisher,
one after the other, one at a time and delays any errors till the all inner and the outer Publishers terminate.

<dl>
<dt><b>Backpressure:</b></dt>
<dd>{@code concatDelayError} fully supports backpressure.</dd>
<dt><b>Scheduler:</b></dt>
<dd>{@code concatDelayError} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param <T> the common element base type
@param sources the Publisher sequence of Publishers
@param prefetch the number of elements to prefetch from the outer Publisher
@param tillTheEnd if true exceptions from the outer and all inner Publishers are delayed to the end
if false, exception from the outer Publisher is delayed till the current Publisher terminates
@return the new Publisher with the concatenating behavior