It is a long time now that NewComputerModern has build-in information for diacritics stacking. I have heard that xetex supports this but I can not make it work. The font is developed with fontforge and as you can see in the attached screenshot, fontforge shows stacking working.
However xelatex just places, say the grave (uni0300) next and not above the character, say uni2C9B (as in screenshot). So I guess I have something wrong in the font that xetex does not like(?) The font currently develops the coptic block for academic needs this is why I use uni2C9B. A sample file is \documentclass{article} \usepackage{fontspec} \setmainfont{NewCM10-Regular.otf} \begin{document} ⲛ̀ \end{document} However the font that contains this character (since it is under development) is here: https://myria.math.aegean.gr/~atsol/tmp/NewCM10-Regular.sfd <https://myria.math.aegean.gr/~atsol/tmp/NewCM10-Regular.sfd> https://myria.math.aegean.gr/~atsol/tmp/NewCM10-Regular.otf <https://myria.math.aegean.gr/~atsol/tmp/NewCM10-Regular.otf> thanks for any help, Antonis.