[XeTeX] Disable "mktextfm" and/or use of TFM-based fonts ?

[Philip Taylor (Hellenic Institute)]

On 08/06/2022 09:55, Ulrike Fischer wrote:
> Sorry but I think it is one of the nice features of a modern tex
> system that it creates tfm or pk fonts on the fly.
That's fine; we can agree to differ on such philosophical points.
> xetex is doing that internally too for your open type fonts: it is
> still tex and needs tfm files.
Does it ?  Are you absolutely certain ?
> Do you want to miss that feature and
> have to prepare the tfm files your self before using a font?
It it does, then no, I am happy for it to do that, but I was unaware 
that it does.
> XeTeX doesn't fallback. It uses the fonts that your format and your
> code tells it to use. If you prefer to use unicode math fonts, here
> is a receipt what you have to change in plain for this:
> https://tex.stackexchange.com/q/308749/2388

By "fall back", I meant "use Computer Modern for maths if Ihave failed 
to declate my own maths fonts".  But thank you for the recipe — much 
appreciated.

Incidentally, I now see that I can use the following successfully, which 
makes it far easier to integrate the desired functionality into TeXwords —

> D:\ XeTeX -no-mktex=TFM \input Font-error
> This is XeTeX, Version 3.141592653-2.6-0.999994 (TeX Live 2022) 
> (preloaded format=xetex)
>  restricted \write18 enabled.
> entering extended mode
> (./Font-error.tex [1] [2] [3] [4] [5] [6] [7] [8] [9]
> ! Font \fnf= not loadable: Metric (TFM) file or installed font not found.
> <to be read again>
>                    \font
> l.441 \font \fnf  = \font
>                           \fb "Gill Sans MT" scaled 455
> ? s
> OK, entering \scrollmode...
> [10] [11] [12] )
> (see the transcript file for additional information)
> Output written on Font-error.pdf (12 pages).
> Transcript written on Font-error.log.
-- 
/** Phil./

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