docs: def ParseConfigCommandLine():
    """Parse all the command line options which control the config system."""
    # The user may specify the primary config file on the command line.
    if flags.FLAGS.config:
      _CONFIG.Initialize(filename=flags.FLAGS.config, must_exist=True)
    else:
      raise RuntimeError("A config file is not specified.")
  
    # Allow secondary configuration files to be specified.
    if flags.FLAGS.secondary_configs:
      for config_file in flags.FLAGS.secondary_configs:
        _CONFIG.LoadSecondaryConfig(config_file)
  
    # Allow individual options to be specified as global overrides.
    for statement in flags.FLAGS.parameter:
      if "=" not in statement:
        raise RuntimeError("statement %s on command line not valid." % statement)
  
      name, value = statement.split("=", 1)
      _CONFIG.global_override[name] = value
  
    # Load additional contexts from the command line.
    for context in flags.FLAGS.context:
      if context:
        _CONFIG.AddContext(context)
  
    if _CONFIG["Config.writeback"]:
      _CONFIG.SetWriteBack(_CONFIG["Config.writeback"])
  
    # Does the user want to dump help? We do this after the config system is
    # initialized so the user can examine what we think the value of all the
    # parameters are.
    if flags.FLAGS.config_help:
      print("Configuration overview.")
  
      _CONFIG.PrintHelp()
      sys.exit(0)