/**
  * This method responds to the contents of tags in a way determined by the name of the tag (as
  * determined by the startElement method).
  */
 public void characters(char[] ch, int start, int length) {
   String contents = new String(ch, start, length);
   if (tag_identifier == 1) classes.add(contents);
   else if (tag_identifier == 2) meta_data_info.add(contents);
   else if (tag_identifier == 3) current_root_classification.identifier = contents;
   else if (tag_identifier == 4) current_root_classification.role = contents;
   else if (tag_identifier == 5)
     current_subset_classification.start = Double.parseDouble(contents);
   else if (tag_identifier == 6) current_subset_classification.stop = Double.parseDouble(contents);
 }