 In contrast, the classification of individual languages within their macrolanguage is standardized, in both ISO 639-3 and the Language Subtag Registry.Script subtags were first added to the Language Subtag Registry when RFC 4646 was published, from the list of codes defined in ISO 15924.They are encoded in the language tag after primary and extended language subtags, but before other types of subtag, including region and variant subtags.