code: func ParseRoller(l *LogRoller, what string, where string) error {
  	if l == nil {
  		l = DefaultLogRoller()
  	}
  	var value int
  	var err error
  	value, err = strconv.Atoi(where)
  	if err != nil {
  		return err
  	}
  	switch what {
  	case directiveRotateSize:
  		l.MaxSize = value
  	case directiveRotateAge:
  		l.MaxAge = value
  	case directiveRotateKeep:
  		l.MaxBackups = value
  	}
  	return nil
  }
docs: // ParseRoller parses roller contents out of c.