I'm running into a problem, but maybe not all hope is lost. For my
Greek stuff, I will sometimes need a "dotbelowcomb" accent. Only very
few fonts have that, but no problem, in mkiv, I can simply take that
from a follback font:
\definefontfallback [GreekFallback] [name:texgyretermesregular]
Now I would like to remap the exclam character to this dotbelowcom.
Again, no problem: with a fea file, I can write a sub rule
sub exclam by dotbelowcomb
but I can't combine both approaches: if the font doesn't have the
character, I get an error about "invalid glyph index." In good old
pdftex, it was possible to define a virtual font for such occasions,
and I seem to remember that there's something similar in mkiv, but I'm
unsure how it can be done. Any pointers?
Thanks, and all best