Hi, how should I go at the Plain TeX level about implementing the following glyph substitution which I formerly expressed in a font feature file: languagesystem DFLT dflt; languagesystem latn dflt; feature oneb { sub one by one.ss01; } oneb; The font is Vollkorn, a Plain LuaTeX file which worked in TL2015 would be \input luaotfload.sty \font\x="Vollkorn:script=latn;language=DFLT;+tlig;featurefile=vollkornlua.fff;+oneb;" \x 123 \bye % Local Variables: % TeX-engine: luatex % End: The glyph for digit 1 is modified and picked in stylistic set 1. I don't want to globally switch to that stylistic set, I am only interested into digit 1. My use case is more with LuaLaTeX+fontspec, but if I am explained a Plain LuaTeX approach I can at least forward to Will Robertson who maintains fontspec and cross my fingers that it trickles down back to me at some point via update of fontspec, or luatex, or luaotfload, ... Please CC to me as although I asked for (temporary) list inscription I might not yet be registered. I am aware of https://mailman.ntg.nl/pipermail/ntg-context/2016/083952.html but can't work it out from there. Jean-François