>> Many-to-one: accent marks, e.g. umlauts >> One-glyph-to-many-unicode-characters: ligatures, e.g. "ff", "fi". > > I don’t see how these two cases are different. An accented glyph like > ⟨ɑ̃⟩ is made up of two Unicode characters, ɑ+◌̃ (U+0251 U+0303); > similarly a ligated glyph like ⟨fi⟩ is made up of the two Unicode > characters f+i (U+0066 U+0069).
The first case is usually handled in the GPOS table; the auto-hinter can only ignore this because the rendering of the components doesn't happen together but in succession. See my other mail that gives both a many-to-one and a one-to many example that might be part of GSUB. Werner