@Override
    public void beginStepping() {
        BeginPipelineSteppingEvent.fire(
                this,
                null,
                receivedSourceLocation.getOptChildType().orElse(null),
                StepType.REFRESH,
                new StepLocation(
                        receivedSourceLocation.getMetaId(),
                        receivedSourceLocation.getPartIndex(),
                        receivedSourceLocation.getRecordIndex()),
                null);
    }
Compare the {@link DataRange}s using on the from/to {@link Location};
stroom-core-client/src/main/java/stroom/data/client/presenter/SourcePresenter.java