\font\f="TeX Gyre Termes" \textfont0=\f \scriptfont0=\f \scriptscriptfont0=\f
$ \mathaccent"0017 c $ \bye This is a plain version of a latex example posted by a user to tex.stackexchange. It shouldn't really do anything sensible (if the font load is adjusted for luatex you get the standard missing character warning) But it gives a fatal internal error This is XeTeX, Version 3.141592653-2.6-0.999993 (TeX Live 2021) (preloaded format=xetex) restricted \write18 enabled. entering extended mode (./aa539a.tex ! Internal error: bad native font flag in `map_char_to_glyph' It doesn't seem to matter much which font is used, I just used TeX Gyre above as a specific example. Could this be adjusted to give a normal TeX warning (or error) ? David
