Hello, In EB Garamond I’ve implemented decomposition for all composed glyphs. For uppercase greek I had to use contextual kerning rules: accents like grave or acute and aspiration marks are placed left of the letter, so the glyph has to be placed more to the right and its advance increased. The code in the feature file looks like this: pos [ Epsilon Eta Iota Rho ]' <79 0 79 0> @grk_tlAcc1; Iota adscriptum needs extra space on the right of the base glyph, so there are position rules for that too: pos Eta' <0 0 200 0> uni0345.cap1; and pos Eta' <79 0 279 0> uni0345.cap1 @grk_tlAcc1; Context (and LuaLaTeX too) doesn’t do the positioning correctly. I’ve prepared a minimal example of uppercase etas. The first row without decomposition, the second decomposed, the third with alternate uni0345.cap1 (iota adscriptum). The first two should look exactly the same: \usemodule[simplefonts] \setmainfont[ebgaramond] \definefontfeature[decomp][ss20=yes] \definefontfeature[iota1][ss20=yes,cv81=1] \starttext ἨἩἪἫἬἭἮἯᾘᾙᾚᾛᾜᾝᾞᾟῌ \par \addff{decomp}ἨἩἪἫἬἭἮἯᾘᾙᾚᾛᾜᾝᾞᾟῌ \par \addff{iota1}ἨἩἪἫἬἭἮἯᾘᾙᾚᾛᾜᾝᾞᾟῌ \par \stoptext I use ss20 for full decomposition because it should be selected by the user explicitly only when needed, while ccmp should be enabled by default. The attached ctx_test.pdf shows its output. The font used can be downloaded at http://georgduffner.at/ebgaramond/fonts/EBGaramond12-Regular.otf. For comparison, there’s a test page at http://georgduffner.at/ebgaramond/etatests.html – current Firefox and Chromium show what is expected. There’s a second testfile at https://github.com/georgd/EB-Garamond/blob/master/tests/context_greektests.t... with the complete Unicode block of greek polyphonic characters, its pdf output is attached to this mail too, a comparison html page is at http://georgduffner.at/ebgaramond/greektests.html Best regards, Georg