vocative: indicate which (experimental) grammar / standard / dialect / language specification is used.
Can be a single feature, or a complete specification or standard of many choices. Can be used after «ko'a broda tau ko'e» to indicate «goi'ai la tcekitau». See also: gi'ai (experimental grammar UI rather than COI), jo'au (change language COI). jo'au specifies a language switch, while goi'ai indicates or makes a claim of what is being used.