Formally define the method of interpreting lookups

[be5invis]

• GSUB
  • How are the substitution performed?
  • How are the cluster map maintained?
• GPOS
  • How are the positioning method maintained?

[mhosken]

These questions are too big and vague to be answered directly. Could you break down your questions?

[be5invis]

@mhosken
I am referring this question that I twitted: https://twitter.com/belleveinvis/status/1072886672444993537

From @tiroj:

Correct. There's never been an implementation specification for OpenType Layout, only a data format specification. Not only is interpretation of lookups not specified, nor is run segmentation and other dependent or dependency-creating aspects.

From @behdad:

There's an implied algorithm but the fine details are not written down in the standard.