In XITS I have stylistic sets (ss01-07) for accessing additional alphabets not bresent in Unicode, or variants of exising ones. For example, ss01 maps the script alphabets to an alternate calligraphic one, so I did: \starttext \setupbodyfont[xits] \ctxlua{fonts.otf.features.register_base_substitution('ss01')} \definefontfeature[ss01][mode=base,script=math,ss01=yes] $\addff{ss01}\cal ABCDEFG$ \stoptext (I was not expecting \addff to work in math, but anyway). This works, however, but I don't want to set the feature globally: \starttext \ctxlua{fonts.otf.features.register_base_substitution('ss01')} \definefontfeature[math-text][mode=base,script=math,ss01=yes] \setupbodyfont[xits] $\cal ABCDEF$ \stoptext Regards, Khaled -- Khaled Hosny Arabic localiser and member of Arabeyes.org team Free font developer