[XeTeX] diacritics stacking using anchor points

[Antonis Tsolomitis]

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.

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