[MPEG-OTSPEC] Why no GPOS10?

[Simon Cozens]

This is more of a historic rationale question than anything else.

GSUB8 was added in OT1.4, giving reverse chaining substitution ("rsub"). 
But at that time there was no parallel addition of reverse chaining 
positioning. I presume at the time there was a discussion about it and a 
good reason why it was not eventually added, but I can't get to any 
opentype mailing list archives.

I'm quite surprised, because knowing the rationale for why it was added 
(glyph selection in Urdu), any discussion would probably have also 
touched on nukta repositioning which has to be done in more or less the 
same way.

Simon