code: private String constructAdditionalNamespacesString(List<AdditionalNamespace> additionalNamespaceList) {
          String result = "";
          if (additionalNamespaceList.contains(AdditionalNamespace.IMAGE)) {
              result += " xmlns:image=\"http://www.google.com/schemas/sitemap-image/1.1\" ";
          }
          if (additionalNamespaceList.contains(AdditionalNamespace.XHTML)) {
              result += " xmlns:xhtml=\"http://www.w3.org/1999/xhtml\" ";
          }
          return result;
      }
docs: Construct additional namespaces string
  @param additionalNamespaceList
  @return