[XeTeX] AAT feature codes

[Will Robertson]

(This didn't appear to get through the first/second/third/fourth time, 
so I've re-sent it. How bizarre!)

Hi Jonathan

This page on the Apple website
http://developer.apple.com/fonts/Registry/index.html
shows all of the AAT features supported as of 1996 or something. I 
assume it's still correct (seems to be). At the bottom it shows the 
numerical codes for each feature:

<snip>
    ligaturesType = 1,
       requiredLigaturesOnSelector          = 0,
       requiredLigaturesOffSelector         = 1,
       commonLigaturesOnSelector            = 2,
       commonLigaturesOffSelector           = 3,
<snip>

This implies to me that choosing the third selection of the first 
feature will turn off Common Ligatures. (And so on with these types of 
things: even means on, odd means off.)

But in XeTeX I see something different - it turns on Common Ligatures 
for both 2 & 3. The sample file at the end (based on code you gave me 
:) demonstrates.

I can't tell if this a bug in XeTeX. If not, it's very easy for me to 
work around.

Many thanks,
Will

%&program=xetex

\nopagenumbers \frenchspacing

\def\testtext{fling fields}

\def\testfontcode#1#2#3{%
   \def\myfont{#1}
   \font\testfont="\myfont" at 10pt
   \edef\featurename{\XeTeXfeaturename\testfont #2 }
   \ifx\featurename\empty
     Font \myfont\ doesn't seem to support this feature.\par
   \else
     \edef\selectionname{\XeTeXselectorname\testfont #2 #3 }
     \ifx\selectionname\empty
       Font \myfont\ doesn't seem to support this selection.\par
     \else
       The feature/selection code #2/#3 is
       the option "\featurename=\selectionname".\par
     \fi
   \fi}

\testfontcode{Hoefler Text}{1}{2}
\testfontcode{Hoefler Text}{1}{3}

I would have thought 1/3 should be "Ligatures=!Common Ligatures"

\end