In Glyphs 3, a vendor feature/private feature/four capital letters feature can not reference lookups defined in GPOS features such as ‘kern’ or ‘mark’. The feature code editor shows not error but the export fails with this message:
Glyphs 2 has no problem exporting the file.
- Test-file (format version 3): Test3.glyphs (6.1 KB, fails in G3)
- Test-file (format version 2): Test2.glyphs (6.1 KB, fails in G3, succeeds in G2)
Looking at the generated features.fea file, the problem seams to be that the vendor feature appears before the GPOS features such as ‘kern’, ‘mark’, etc. even though it is placed after them in the features list in the “Features” tab.