src/main/java/io/reactivex/Completable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
    public static Completable mergeDelayError(Publisher<? extends CompletableSource> sources) {
        return merge0(sources, Integer.MAX_VALUE, true);
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
    public static Completable mergeDelayError(Publisher<? extends CompletableSource> sources) {
        return merge0(sources, Integer.MAX_VALUE, true);
    }
Returns a Completable that subscribes to all Completables in the source sequence and delays
any error emitted by either the sources observable or any of the inner Completables until all of
them terminate in a way or another.
<p>
<img width="640" height="466" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Completable.mergeDelayError.p.png" alt="">
<dl>
<dt><b>Backpressure:</b></dt>
<dd>The returned {@code Completable} honors the backpressure of the downstream consumer
and expects the other {@code Publisher} to honor it as well.</dd>
<dt><b>Scheduler:</b></dt>
<dd>{@code mergeDelayError} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
@param sources the sequence of Completables
@return the new Completable instance
@throws NullPointerException if sources is null