[XeTeX] XeTeX and "ignore sub" substitution rules

[Apostolos Syropoulos]

> It appears to me that XeTeX doesn't handle, at all, OpenType context
> substitutions that match without doing a substitution - i.e. the ones that
> appear in Adobe feature files as "ignore sub" rules.  When one of 
> these

Well I don't really agree.I have included the following feature in a font
that I am working and it works just fine with XeTeX:


@calt1 = [ Omicron.calt Epsilon.calt Alpha.calt alpha.calt epsilon.calt omicron.calt ]; 
@calt2 = [ Alphatonos Epsilontonos Omicrontonos alphatonos epsilontonos omicrontonos  
           uni1F04 uni1F0C uni1F14 uni1F1C uni1F44 uni1F4C ]; 
@calt3 = [Alphatonos Epsilontonos Etatonos Iotatonos Omicrontonos Upsilontonos Omegatonos  
          ............................................................................  
          uni1FF3 uni1FF4 uni1FF6 uni1FF7 uni1FF8 uni1FF9 uni1FFA uni1FFB uni1FFC ]; 
 
feature calt { # Contextual Alternates 
 ......................
 script grek; # Greek 
    ignore sub @calt3 etatonos'; 
    ignore sub etatonos' @calt3; 
    sub etatonos' by etatonos.calt; 
    ignore sub @calt3 uni1F22'; 
    ignore sub uni1F22' @calt3; 
    sub uni1F22' by uni1F22.calt; 
    sub @calt2' [iota upsilon] by [Alpha.calt Epsilon.calt Omicron.calt alpha.calt epsilon.calt omicron.calt alpha.calt Alpha.calt epsilon.calt Epsilon.calt omicron.calt Omicron.calt]; 
    sub @calt1 [iota upsilon]' by [iotadieresis.calt upsilondieresis.calt]; 
} calt; 


A.S.

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Apostolos Syropoulos
Xanthi, Greece