[XeTeX] Syriac abbreviations, and issues with polyglossia, fontspec and bidi

[Gareth Hughes]

I think this is firstly a font issue, but I don't know exactly what's
causing it, but there is also an additional Fontspec issue.

In Syriac, abbreviations and numerals can be marked by an overline. For
abbreviations, the overline often extends over the last few letters of
the abbreviation. This overline is supposed to be invoked by the Unicode
character U+070F Syriac Abbreviation Mark = SAM, but I cannot get the
Meltho fonts (specifically the Serto fonts are relevant here) to support
it properly. I'm told that the Meltho fonts display the abbreviation
mark correctly in MS Word. Here's a minimal example:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\documentclass{minimal}
\usepackage{polyglossia}
\setmainlanguage{syriac}
\usepackage{xltxtra}
\setmainfont[Script=Syriac]{Serto Jerusalem}
\newcommand\test{ܬ܏ܫܒܘ}
\begin{document}
\noindent\test\\
\fontspec[Script=Syriac]{Serto Batnan}\test\\
\fontspec[Script=Syriac]{Serto Kharput}\test\\
\fontspec[Script=Syriac]{Serto Malankara}\test\\
\fontspec[Script=Syriac]{Serto Mardin}\test\\
\fontspec[Script=Syriac]{Serto Urhoy}\test
\end{document}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

The other issues are that

1) I now have to load xltxtra.sty after \setmainlanguage{syriac} because
the latter calls bidi.sty, which now needs to be loaded first. The old
version of bidi.sty I was using could be loaded last.

2) I had to repeat [Script=Syriac] for every font so that the correct
ligatures are made. I would have thought that
\defaultfontfeatures{Script=Syriac} would set the feature in one go, but
I get the error "Package xkeyval Error: `Script' undefined in families
`options'" if I try this.

Thanks,

Gareth.