[XeTeX] XETEX cannot access OpenType features in PUA?

[Jonathan Kew]

On 27 Nov 2011, at 23:07, mskala at ansuz.sooke.bc.ca wrote:

> On Sun, 27 Nov 2011, Aleksandr Andreev wrote:
>> It appears that XeTeX colors are handled by inserting pdfliteral nodes
>> around colored items, which breaks the access to GPOS.
>> 
>> Unless there's been some work on this issue since 2007, it appears
>> that I will need to look for a different way of typesetting my
>> document.
> 
> I bet you'll see similar effects on other systems, too.  I'm actually
> surprised that Firefox seems to work the way you want it to; I've seen
> (for instance, in the page at
> http://www.uni-graz.at/~katzer/korean_hangul_unicode.html - right now I'm
> working on implementing conjoining behaviour of Korean letters via GSUB)
> HTML markup being used explicitly for the purpose of breaking up glyph
> sequences that would otherwise be subject to Unicode conjoining
> behaviour, and I would expect it to usually have that effect.  If there's
> a "style" of any kind applied to one glyph and not to the previous glyph,
> there's good chance that software in general, not just XeTeX, will break
> the glyph sequence and not see substitution rules that would apply to the
> glyphs if they were really adjacent.  If it's important to be able to
> style one glyph and not another, then I think you're asking for trouble to
> also depend on a substitution rule matching them both.

Right - in general this is hard to implement, and most software doesn't try. Firefox goes to some lengths to make this work properly for style changes (such as color or underlining) that do not inherently need to affect glyph shaping.

Making this work in xetex would require a different approach to implementing color.

JK