[MPEG-OTSPEC] Many to many substitution and localization

[Simon Cozens]

On 26/09/2024 18:04, William_J_G Overington via mpeg-otspec wrote:
> Can this idea become implemented please?

The short answer is no.

Suppose a many-to-many substitution is implemented with the lookupflag 
of "IgnoreMarks", and suppose also that there are marks in the input 
glyph sequence. It's not possible to determine how those marks should be 
distributed amongst the new set of glyphs produced by the substitution.

It's possible to do what you're asking for by first ligating glyphs into 
a single glyph ("sub exclam nine eight three by word_983") and then 
using a multiple substitution to perform the localisation ("sub word_983 
by D i o l c h ...") (Of course, the fact that you can do it does not 
mean you should.) So in practice, many-to-many substitution is often 
unneeded.


S