>> 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
