It's defined in typo-fkr.lua, but I can't understand what parameters to pass and whether it's the right macro. It looks like it's not. look at the extension examples in the test suite: you can define a kern

On 4/5/2022 1:45 PM, mf via ntg-context wrote: pair positioning feature than you enable for just that font Hans ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl -----------------------------------------------------------------

There's a problem with oldstyle glyphs, because they have different codes inside a font. I used fontforge to find the "four.oldstyle" glyph, whose code is 0xf734. But then I discovered that the 'four.oldstyle' key works the same in the lua table. This is the updated MWE, suitable for oldstyle glyphs too. -------------------------------------------------- \mainlanguage[it] % modified from http://www.pragma-ade.com/context/latest/cont-tst.zip % file: doc/context/tests/mkiv/fonts/extensions-001.tex \startluacode fonts.handlers.otf.addfeature { name = "ktest", type = "kern", data = { [ '’' ] = { [ '4' ] = -100, [ 0xf734 ] = -150, -- four.oldstyle code -- [ 'four.oldstyle' ] = -150, -- this is the same as the previous line }, } } \stopluacode \definefontfeature[ktest][ktest=yes] \definefontfeature[onum][onum=yes] \starttext Default: «Questo è successo nel ’48». Desired: «Questo è successo nel ’\kern-.1em 48». Solved: \feature[+][ktest]«Questo è successo nel ’48». Onum: \feature[+][onum]«Questo è successo nel ’48». \stoptext -------------------------------------------------- Massi