Learn testLateDataAccumulating

[上海_技术部_数据平台_唐觊隽]

I am looking the testLateDataAccumulating method in CreateStreamTest.But I 
can’t unstand the code reded .

    PCollection<Integer> windowed = p
        .apply(source)
        
.apply(Window.<Integer>into(FixedWindows.of(Duration.standardMinutes(5))).triggering(
            AfterWatermark.pastEndOfWindow()
                .withEarlyFirings(AfterProcessingTime.pastFirstElementInPane()
                    .plusDelayOf(Duration.standardMinutes(2)))
                .withLateFirings(AfterPane.elementCountAtLeast(1)))
            .accumulatingFiredPanes()
            .withAllowedLateness(Duration.standardMinutes(5), 
Window.ClosingBehavior.FIRE_ALWAYS));

Can anyone helps unstanding these triggers?