code: @Override
      public void startElement(final String uri, final String localName, final String qName, final Attributes atts)
              throws SAXException {
          final String cls = atts.getValue(ATTRIBUTE_NAME_CLASS);
          final String id = atts.getValue(ATTRIBUTE_NAME_ID);
  
          if (skip && skipLevel > 0) {
              skipLevel++;
          }
  
          if (TOPIC_TOPIC.matches(cls)) {
              topicSpecSet.add(qName);
  
              processSelect(id);
          }
  
          if (include) {
              includelevel++;
              final Attributes resAtts = processAttributes(atts);
              writeStartElement(output, qName, resAtts);
          }
      }
docs: SAX methods