src/main/java/io/reactivex/Flowable.java
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Flowable<T> concatDelayError(Publisher<? extends Publisher<? extends T>> sources) {
        return concatDelayError(sources, bufferSize(), true);
    }
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Flowable<T> concatDelayError(Publisher<? extends Publisher<? extends T>> sources) {
        return concatDelayError(sources, bufferSize(), true);
    }
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
@return the new Publisher with the concatenating behavior