OFF "cv01"-"cv99", and a more general question

[karstenluecke]

Hello Mr Constable and Thomas,

thank you for the clarification regarding "cvXX" and "ssXX".
I have ignored the mention of lookup type 3 in the spec. So this means that "cvXX" features are applied only to single selected characters/glyphs rather than entire paragraphs. Then it makes sense indeed that no more than one "cvXX" feature would address a specific character/glyph.
(My earlier interpretation was that it would really behave like "ssXX": Select a string of text in the application, then choose "cv01" to replace all "a"s by a variant, choose "cv02" to replace all "n"s by a variant, etc.)

* * *

> Also, the comparison at this point is not an apples-to-apples
> comparison: [...]
> I think a more even comparison with GX layout and ATSUI
> would be GDI text, WPF, DirectWrite or similar APIs

This is true, and possibly helps me make my point clear:
GX aims at a single platform for which an according engine/API is available. So within this limited realm the couple of font format and engine/API exists.
OpenType claims to be platform independent (this is how it was sold to foundries and end users, and only then it makes sense to turn it into a standard), but there is no cross-platform engine/API nor a specification which would ensure that OT fonts, built after the spec, behave the same on a variety of platforms.
(No intentions to play out GX vs OT. GX just helps me illustrate what I consider as important missing bit.)

Best wishes,
Karsten