docs: public static boolean isValid(String token)
      {
          if (token == null || token.length() == 0)
          {
              return false;
          }
  
          int len = token.length();
  
          for (int i = 0; i < len; ++i)
          {
              if (isSeparator(token.charAt(i)))
              {
                  return false;
              }
          }
  
          return true;
      }