docs: static String buildVirtualPageTitle(Map<String, String> metadata) {
      checkNotNull(metadata);
      List<String> escapedMetadata = new ArrayList<>();
      for (Map.Entry<String, String> entry : metadata.entrySet()) {
        escapedMetadata.add(METADATA_ESCAPER.escape(entry.getKey()) + "="
            + METADATA_ESCAPER.escape(entry.getValue()));
      }
      return Joiner.on(",").join(escapedMetadata);
    }