code: private static boolean serialDocInclude(Doc doc) {
          if (doc.isEnum()) {
              return false;
          }
          Tag[] serial = doc.tags("serial");
          if (serial.length > 0) {
              String serialtext = StringUtils.toLowerCase(serial[0].text());
              if (serialtext.indexOf("exclude") >= 0) {
                  return false;
              } else if (serialtext.indexOf("include") >= 0) {
                  return true;
              }
          }
          return true;
      }
docs: Return true if the given Doc should be included
  in the serialized form.
  
  @param doc the Doc object to check for serializability.