[NTG-context] features of fallback font

Dear List, I'm using the chinese simsun font that has no builtin SerifBold. I'm trying to define a fakebold feature for it, but the following code does not work: \definefontfeature[fakebold][effect={width=0.3, delta=0}] \definefontfallback [sunfallback] [name:simsun] [cjkunifiedideographs] \definefontfallback [sunbffallback] [name:simsun] [cjkunifiedideographs][features=fakebold] \definefontsynonym [Serif] [modern] [fallbacks=sunfallback] \definefontsynonym [SerifBold] [modern] [fallbacks=sunbffallback] \starttext 人 foo \bf 人 bar % bar is bold, the second 人 is not \stoptext Does anyone know how to define features for fallback font? Thanks! Best, Sylvain