@Override
    public void setDocumentLocator(final Locator locator) {
        super.setDocumentLocator(locator);
        writeln(SET_DOCUMENT_LOCATOR);
    }
@param locator an object that can return the location of any SAX document
               event
@see org.xml.sax.Locator
stroom-pipeline/src/main/java/stroom/pipeline/filter/TestSAXEventFilter.java