code: def check_update ():
      
      version, value = get_online_version()
      if version is None:
          # value is an error message
          return False, value
      if version == CurrentVersion:
          # user has newest version
          return True, None
      if is_newer_version(version):
          # value is an URL linking to the update package
          return True, (version, value)
      # user is running a local or development version
      return True, (version, None)
docs: Return the following values:
         (False, errmsg) - online version could not be determined
         (True, None) - user has newest version
         (True, (version, url string)) - update available
         (True, (version, None)) - current version is newer than online version