parameters in metafont files

[Janek Warchoł]

Hi again :)

Congrats on 0 criticals!

I have a question about parameters in metafont files: i want to create something similar to mf/out/feta20.otf-table, but i don't understand how it's done (i tried to find "bbox" and "attachment" in mf files or scripts/build/gen-emmentaler-scripts.py, but there are no results). I also tried adding

autometric_parameter ("someBogusName", someValue);
inside mf code, but there were no results.
Here is roughly what i want to achieve:
add a magical command to feta-flags.mf

fet_beginchar ("8th Flag (up)", "u3");

[...] % flags.u3 definition 
magical_command (arbitraryRealValueChosenByMe);
fet_endchar;

fet_beginchar ("16th Flag (up)", "u4");
[...] % flags.u4 definition 
magical_command (anotherArbitraryRealValueChosenByMe);
fet_endchar;

[...]

and have it output a flags.otf-table file looking like this

(flags .
(u .
((3 . (arbitraryRealValueChosenByMe))
(4 . (anotherArbitraryRealValueChosenByMe))
[...] ))
.
(d .
[...] )))

Please help!
Janek