docs: private static boolean isValidBrace(String url) {
          if (null == url || url.trim().length() == 0) {
              return false;
          }
  
          boolean isInsideVariable = false;
          StringTokenizer tokenizer = new StringTokenizer(url, "{}", true);
          while (tokenizer.hasMoreTokens()) {
              String token = tokenizer.nextToken();
              if (token.equals("{")) {
                  // { is not allowed inside of a variable specification
                  if (isInsideVariable) {
                      return false;
                  }
                  isInsideVariable = true;
              } else if (token.equals("}")) {
                  // } must be preceded by {;
                  if (!isInsideVariable) {
                      return false;
                  }
                  isInsideVariable = false;
              }
          }
          return true;
      }