docs: public static String getElementID(final String relativePath) {
          final String fragment = FileUtils.getFragment(relativePath);
          if (fragment != null) {
              if (fragment.lastIndexOf(SLASH) != -1) {
                  final String id = fragment.substring(fragment.lastIndexOf(SLASH) + 1);
                  return id.isEmpty() ? null : id;
              }
          }
          return null;
      }