[MPEG-OTSPEC] Documentation guidance on CFF(2) transformation

[Skef Iterum]

I was looking through the COLR portions of the spec and didn't find any 
guidance on applying transformations to CFF or CFF2 glyph sources, what 
with those formats various horizontal- and vertical- specific operators.

Was it assumed that implementations would first unpack into some 
intermediate form, such as moveto/lineto/curveto sequences, and thus no 
further guidance was needed? (Obviously COLR does work with CFF and 
CFF2, so one assumes, or hopes, that the implementations sorted all this 
out.) Or is it more that one can just expect that implementers will 
figure this sort of thing out in general, and if so how does one decide 
what needs some guidance and what doesn't?

Additionally, would such assumptions still apply to VARC, where more of 
the operator-specific data (such as flex hints -- although I don't plan 
to argue that CFF flex hints are particularly relevant in 2023) might 
need to be preserved in some form through some transformations?

Skef