Description
I'm surprised at what I think I'm seeing. Please correct me if I'm wrong.
Part of the CFF2 spec says:
By default, the first ItemVariationData structure (index 0) will be used. The vsindex operator can be used for glyphs that require a different list of regions.
But then there's text that says:
The vsindex key may be used in a PrivateDICT to select a different list of regions for the group of glyphs associated with that PrivateDICT. vsindex may also be used in a CharString to select the list of regions for that glyph. When used in a CharString, it overrides a setting in the associated PrivateDICT.
And in another place:
When used within a PrivateDICT, it has effect not only for variation of values specified by PrivateDICT keys but also for variation in all CharStrings associated with that PrivateDICT. However, a vsindex operator can also be used within a CharString, taking precedence over the vsindex specified in the PrivateDICT.
Humm. So, which is it. If a CharString doesn't have a vsindex operator, is the first ItemVariationData structure (index 0) used, or the vsindex specified in the PrivateDICT is used? Looks like the intention is the latter. I find the first quotation above misleading and suggest changing it to say that it defaults to 0 in the PrivateDICT case only.
I think I have unfortunately written some code, either in FontTools or HarfBuzz, that assumes that vsindex defaults to 0 in CharString processing.