reactor-core/src/main/java/reactor/core/publisher/Flux.java
public final Flux<Flux<T>> windowUntil(Predicate<T> boundaryTrigger, boolean cutBefore, int prefetch) {
		return onAssembly(new FluxWindowPredicate<>(this,
				Queues.unbounded(prefetch),
				Queues.unbounded(prefetch),
				prefetch,
				boundaryTrigger,
				cutBefore ? FluxBufferPredicate.Mode.UNTIL_CUT_BEFORE : FluxBufferPredicate.Mode.UNTIL));
	}
public final Flux<Flux<T>> windowUntil(Predicate<T> boundaryTrigger, boolean cutBefore, int prefetch) {
		return onAssembly(new FluxWindowPredicate<>(this,
				Queues.unbounded(prefetch),
				Queues.unbounded(prefetch),
				prefetch,
				boundaryTrigger,
				cutBefore ? FluxBufferPredicate.Mode.UNTIL_CUT_BEFORE : FluxBufferPredicate.Mode.UNTIL));
	}
Split this {@link Flux} sequence into multiple {@link Flux} windows delimited by the given
predicate and using a prefetch. A new window is opened each time the predicate
returns true.
<p>
Windows are lazily made available downstream at the point where they receive their
first event (an element is pushed, the window completes or errors).
<p>
If {@code cutBefore} is true, the old window will onComplete and the triggering
element will be emitted in the new window. This variant can emit an empty window
if the sequence starts with a separator.
<p>
Otherwise, the triggering element will be emitted in the old window before it does
onComplete, similar to {@link #windowUntil(Predicate)}. This variant shouldn't
expose empty windows, as the separators are emitted into the windows they close.
<p>
<img class="marble" src="doc-files/marbles/windowUntilWithCutBefore.svg" alt="">

@reactor.discard This operator discards elements it internally queued for backpressure
upon cancellation or error triggered by a data signal.

@param boundaryTrigger a predicate that triggers the next window when it becomes true.
@param cutBefore set to true to include the triggering element in the new window rather than the old.
@param prefetch the request size to use for this {@link Flux}.
@return a {@link Flux} of {@link Flux} windows, bounded depending
on the predicate.