Thank you Hans for your example:
so I'm looking for an automatic way to replace every "È" in the text with "\smash{È}".
\definefontfeature[default][default][dimensions={0,1.9,0}]
It took a while to understand how it works but it was worthy. I try to summarize because others may find it useful: - the "dimensions" feature is defined in font-ext.lua - its parameters modify the footprint of the glyphs of a font - its parameters are factors for glyph's width, height (over the baseline) and depth (under the baseline) - they are factors of emwidth, exheight and exheight respectively - a value of zero for any of them means "leave the default value untouched", dimensions={0,1.9,0} means that only the height of (the footprint of) glyphs is set to 1.9 times exheight, the other two dimensions stay untouched Before looking at the code I started playing with the dimensions values to understand what they controlled. One trial was this \definefontfeature[default][default][dimensions={2,0,0}] I got "spaced" text (glyphs have a larger footprint and appear spaced) But this does not work: \definefontfeature[spaced][dimensions={2,0,0}] \starttext Normal text and {\feature[+][spaced]spaced text} \stoptext Is it a feature that works only globally?