code: @CheckReturnValue
      @SchedulerSupport(SchedulerSupport.NONE)
      public static <T> Observable<T> concatDelayError(Iterable<? extends ObservableSource<? extends T>> sources) {
          ObjectHelper.requireNonNull(sources, "sources is null");
          return concatDelayError(fromIterable(sources));
      }
docs: Concatenates the Iterable sequence of ObservableSources into a single sequence by subscribing to each ObservableSource,
  one after the other, one at a time and delays any errors till the all inner ObservableSources terminate.
  <p>
  <img width="640" height="380" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/concatDelayError.png" alt="">
  <dl>
  <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 Iterable sequence of ObservableSources
  @return the new ObservableSource with the concatenating behavior