code: func (p *PEMFile) Set(value string) error {
  	contents, err := ioutil.ReadFile(value)
  	if err != nil {
  		return err
  	}
  	if pemBlock, _ := pem.Decode(contents); pemBlock == nil {
  		return errors.New("file contents must be in PEM format")
  	}
  	p.contents, p.path = string(contents), value
  	return nil
  }
docs: // Set parses a root rotation option