Due to a question on tex.sx (https://tex.stackexchange.com/questions/452969/luatex-fontfeaturefractions-o...) I looked again (see https://www.mail-archive.com/ntg-context@ntg.nl/msg84822.html) at the frac feature. The output is still not really satisfactory. With mode=node numbers with slash looks okay, but single numbers are rather odd: only the last digit has the correct size: \starttext \font\test={file:linlibertine_r.otf:mode=node;script=latn;language=DFLT;+frac} \test 787347 125 1/7 1/2 3/4 5/6 7/8 9/10 11/12 31415/27182 1000/1000000 \font\test={file:linlibertine_r.otf:mode=base;script=latn;language=DFLT;+frac} \test 787347 125 1/7 1/2 3/4 5/6 7/8 9/10 11/12 31415/27182 1000/1000000 \stoptext (It could be a font bug, the output with xetex isn't good either). -- Ulrike Fischer https://www.troubleshooting-tex.de/