[NTG-context] Furigana

Dear CJK experts, I am looking to add furigana (readings) above the Kanji (Chinese characters) in a Japanese text. In XeTeX I'd be used to something translating to \usemodule[simplefonts] \usemodule[ruby] \starttext \ruby{今日}{こんにち}は \stoptext What would be the correct command for mkiv? Many thanks. Severin