docs: private static void addCacheFormatEntry(List<Message> trackListEntries, int playlistId, ZipOutputStream zos) throws IOException {
          // Add a marker so we can recognize this as a metadata archive. I would use the ZipFile comment, but
          // that is not available until Java 7, and Beat Link is supposed to be backwards compatible with Java 6.
          // Since we are doing this anyway, we can also provide information about the nature of the cache, and
          // how many metadata entries it contains, which is useful for auto-attachment.
          zos.putNextEntry(new ZipEntry(CACHE_FORMAT_ENTRY));
          String formatEntry = CACHE_FORMAT_IDENTIFIER + ":" + playlistId + ":" + trackListEntries.size();
          zos.write(formatEntry.getBytes("UTF-8"));
      }