Referring to this tread:https://typedrawers.com/discussion/1319/opentype-aalt-feature
I don't understand the two types of lookups that it is possible / convenient (or not?) to carry out.
I refer to the fonts that I saw that present two aalt lookups, the first one of "single substitution" type, the second one of "alternate substitution".
Type 1 is simple: it involves setting a 1: 1 substitution.
As far as type 3 is concerned, the concept of <glyphclass> (or "group") is not clear to me.
In the first lookup (single replacement) I find for example the glyphs of lowercase letters and the replacement with the small caps version (i.dot -> i.dotsc.
In the second lookup (alternate substitution) the glyphs of letters that are passable of innumerable substitutions (i -> i.superior i.inferior .dot i.sc).But then what are the glyphclasses with only one member?