Which is the logic and the order in kerning tables?
Let's make a hypothesis. I intend to create three different kerning tables inside the same Lookup, the first one for the letters (pairs as `AV`, `To`, `Fr` etc.), the second one for the punctuation (pairs as `W.` `T-` `F,` etc), the third one for the numbers. Should they be placed in a predefined order?
My problem is that if I create a `'kern' Horizontal Kernin lookup 1` and then two subtables, i.e. `'kern' Horizontal Kerning lookup 1 kerning class 1` and then `'kern' Horizontal Kerning lookup 1 kerning class 2`, only the first is applied. If it is reversed, same thing. The first one is applied, the second one ignored.
Have I to create different lookups (and not different subtables in the same lookup)?
Or there is a conflict if in the first subtable I have `WA` and in the second `W.' ? But are they summative?
Now I ask: what's wrong in my procedure? How can the problem be solved, perhaps keeping the various subtables distinct?
It was necessary to place both the lookups of the kerning of the apostrophe before the general kerning of the letters.
I'd like to understand why ...
For example in Word 'A (quote A) will be changed to
'A (quoteleft A)
while L' (L quote) is changed to
L' (L quoteright)
But, pratically, for instance, I write:
l'America : kerning between ' and A
L'automobile: kerning between L and '
L'AMERICA. requested double kerning between L' and 'A
How can I set the table?
In GaramondPremierePro there is a Lookup with a first subtable (lookup 1 kerning class 1) with kerning for quoteright (left column) and letters as A, F and L (right column). A second subtable (lookup 1 kerning class 4) with kerning for letters as A, L and F (left column) and quoteright (right column). Is this the correct approach?
Some fonts have a kerning table for letters, another one for numbers.
Is there any other substantial reason besides a simple principle of order?