code: func (t *TraceLocation) Set(value string) error {
  	if value == "" {
  		// Unset.
  		t.line = 0
  		t.file = ""
  	}
  	fields := strings.Split(value, ":")
  	if len(fields) != 2 {
  		return errTraceSyntax
  	}
  	file, line := fields[0], fields[1]
  	if !strings.Contains(file, ".") {
  		return errTraceSyntax
  	}
  	v, err := strconv.Atoi(line)
  	if err != nil {
  		return errTraceSyntax
  	}
  	if v <= 0 {
  		return errors.New("negative or zero value for level")
  	}
  	t.line = v
  	t.file = file
  	return nil
  }
docs: // Syntax: gopherflakes.go:234
  // Note that unlike vmodule the file extension is included here.