src/main/java/io/reactivex/Observable.java
@SuppressWarnings({ "unchecked", "rawtypes" })
    @CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Observable<T> mergeDelayError(ObservableSource<? extends T> source1, ObservableSource<? extends T> source2, ObservableSource<? extends T> source3) {
        ObjectHelper.requireNonNull(source1, "source1 is null");
        ObjectHelper.requireNonNull(source2, "source2 is null");
        ObjectHelper.requireNonNull(source3, "source3 is null");
        return fromArray(source1, source2, source3).flatMap((Function)Functions.identity(), true, 3);
    }
@SuppressWarnings({ "unchecked", "rawtypes" })
    @CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Observable<T> mergeDelayError(ObservableSource<? extends T> source1, ObservableSource<? extends T> source2, ObservableSource<? extends T> source3) {
        ObjectHelper.requireNonNull(source1, "source1 is null");
        ObjectHelper.requireNonNull(source2, "source2 is null");
        ObjectHelper.requireNonNull(source3, "source3 is null");
        return fromArray(source1, source2, source3).flatMap((Function)Functions.identity(), true, 3);
    }
Flattens three ObservableSources into one ObservableSource, in a way that allows an Observer to receive all
successfully emitted items from all of the source ObservableSources without being interrupted by an error
notification from one of them.
<p>
This behaves like {@link #merge(ObservableSource, ObservableSource, ObservableSource)} except that if any of the merged
ObservableSources notify of an error via {@link Observer#onError onError}, {@code mergeDelayError} will refrain
from propagating that error notification until all of the merged ObservableSources have finished emitting
items.
<p>
<img width="640" height="380" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/mergeDelayError.png" alt="">
<p>
Even if multiple merged ObservableSources send {@code onError} notifications, {@code mergeDelayError} will only
invoke the {@code onError} method of its Observers once.
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code mergeDelayError} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param <T> the common element base type
@param source1
an ObservableSource to be merged
@param source2
an ObservableSource to be merged
@param source3
an ObservableSource to be merged
@return an Observable that emits all of the items that are emitted by the source ObservableSources
@see <a href="http://reactivex.io/documentation/operators/merge.html">ReactiveX operators documentation: Merge</a>