[XeTeX] XeTeX and "ignore sub" substitution rules

[Khaled Hosny]

On Tue, Nov 29, 2011 at 08:05:35AM -0600, mskala at ansuz.sooke.bc.ca wrote:
> I will attempt to navigate ICU's bug tracking system and submit the bug to
> them.  I don't know if XeTeX's practice is to track updates of ICU, though.

I think TeXLive updates ICU and other packages in its yearly release,
and even if they didn't I think you can convince them to update it once
that issue is fixed upstream.

> Unfortunately, it appears that in the short term I have to not only do
> without "ignore sub," but also do without later rules seeing the output of
> earlier rules, because I need my fonts to work both with widely-deployed
> XeTeX and with correct implementations.

In my experience ICU's layout engine have several other OpenType issues,
especially with not widely used parts of the spec. Long ago there was a
plan to replace their own implementation with HarfBuzz, no idea if this
still true.

Regards,
 Khaled