code: func FilterByIssuer(iss string) (CertificateFilter, error) {
  	issFilter, err := regexp.Compile(iss)
  	if err != nil {
  		return nil, err
  	}
  
  	return func(cm *CertificateMetadata) bool {
  		return issFilter.MatchString(cm.Issuer)
  	}, nil
  }
docs: // FilterByIssuer is a CertificateFilter that returns true if the
  // Issuer in a certificate matches the regular expression passed in.