code: public static Flux<Long> interval(Duration period, Scheduler timer) {
  		return onAssembly(new FluxInterval(period.toMillis(), period.toMillis(), TimeUnit.MILLISECONDS, timer));
  	}
docs: Create a {@link Flux} that emits long values starting with 0 and incrementing at
  specified time intervals, on the specified {@link Scheduler}. If demand is not
  produced in time, an onError will be signalled with an {@link Exceptions#isOverflow(Throwable) overflow}
  {@code IllegalStateException} detailing the tick that couldn't be emitted.
  In normal conditions, the {@link Flux} will never complete.
  <p>
  <img class="marble" src="doc-files/marbles/interval.svg" alt="">
  
  @param period the period {@link Duration} between each increment
  @param timer a time-capable {@link Scheduler} instance to run on
  
  @return a new {@link Flux} emitting increasing numbers at regular intervals