[luatex] Opentype init/medi/fina.

[Paul Isambert]

Le 02/06/2011 13:06, Arthur Reutenauer a écrit :
>>   The init, medi and fina tags in OT fonts set variants of glyphs
>> according to position (used by arabic fonts or scripts). Now you'd
>> think it's a contextual substitution.
>    No, it's really not.  The layout engine is responsible for contextual
> analysis, and has to decide what feature to apply, if any.

So that such an analysis must be done depends only on the tags 
themselves? I.e. you have to know that even though init and e.g. smcp 
point to similar lookups (simple substitution), they shouldn't be 
treated similarly: in the case of smcp, the lookup suffices, while in 
the case of init it doesn't. It is surprising that nothing in the font 
signals such a difference... but now I discover Microsoft says so 
clearly (http://www.microsoft.com/typography/otspec/featuretags.htm), 
mentioning precisely the init tag!

Best,
Paul