code: func CanonicalIdentifier(identifier string) string {
  	base, params, err := mime.ParseMediaType(identifier)
  	if err != nil {
  		return identifier
  	}
  	id := base
  	if i := strings.Index(id, "+"); i != -1 {
  		id = id[:i]
  	}
  	return mime.FormatMediaType(id, params)
  }
docs: // CanonicalIdentifier returns the media type identifier sans suffix
  // which is what the DSL uses to store and lookup media types.