RFC 5645 and RFC 5646 added primary language subtags corresponding to ISO 639-3 codes for all languages that did not already exist in the Registry. In addition, codes for languages encompassed by certain macrolanguages were registered as extended language subtags. Sign languages were also registered as extlangs, with the prefix "sgn". These languages may be represented either with the subtag for the encompassed language alone ("cmn" for Mandarin) or with a language-extlang combination ("zh-cmn"). The first option is preferred for most purposes. The second option is called "extlang form" and is new in RFC 5646.