docs: public static void validateId(final String id) {
      if (id == null || id.isEmpty()) {
        throw new IllegalArgumentException("The ID cannot be null or empty");
      }
      for (int i = 0; i < id.length(); i++) {
        final char c = id.charAt(i);
        if (!(Character.isLetterOrDigit(c))) {
          throw new IllegalArgumentException("Invalid id (\"" + id + 
              "\"): illegal character: " + c);
        }
      }
      if (id.length() == 1) {
        if (Character.isDigit(id.charAt(0))) {
          throw new IllegalArgumentException("The ID cannot be an integer");
        }
      }
    }