code: private void writeHeader(Writer writer)throws IOException {
          writer.write(ICAL_BEGIN);
          writer.write(COLON);
          writer.write(ICAL_VTIMEZONE);
          writer.write(NEWLINE);
          writer.write(ICAL_TZID);
          writer.write(COLON);
          writer.write(tz.getID());
          writer.write(NEWLINE);
          if (tzurl != null) {
              writer.write(ICAL_TZURL);
              writer.write(COLON);
              writer.write(tzurl);
              writer.write(NEWLINE);
          }
          if (lastmod != null) {
              writer.write(ICAL_LASTMOD);
              writer.write(COLON);
              writer.write(getUTCDateTimeString(lastmod.getTime()));
              writer.write(NEWLINE);
          }
      }
docs: /*
  Write the opening section of the VTIMEZONE block