@Override
    public void setDocumentLocator(final Locator locator) {
        super.setDocumentLocator(locator);
        if (locationHolder != null) {
            locationHolder.setDocumentLocator(locator, splitCount);
        }
    }
This method tells filters that a stream is about to be parsed so that
they can complete any setup necessary.
stroom-pipeline/src/main/java/stroom/pipeline/filter/SplitFilter.java