code: func (f *FlagSet) Parse(arguments []string) error {
  	f.parsed = true
  	f.args = make([]string, 0, len(arguments))
  	err := f.parseArgs(arguments)
  	if err != nil {
  		switch f.errorHandling {
  		case ContinueOnError:
  			return err
  		case ExitOnError:
  			os.Exit(2)
  		case PanicOnError:
  			panic(err)
  		}
  	}
  	return nil
  }
docs: // Parse parses flag definitions from the argument list, which should not
  // include the command name.  Must be called after all flags in the FlagSet
  // are defined and before flags are accessed by the program.
  // The return value will be ErrHelp if -help was set but not defined.