[XeTeX] Add Tibe-tan typesetting ability

[Lobsang Sonam]

Hi, dear friends,

	First a delayed greeting for the new year of 2008!

	I'd finished the first version of my preprocess to feed its output to XeTeX/XeLaTeX to typesetting Tibe-tan scripts a few days before, which use discretionary to get certain punctuation changed when appear near the head of a line. Thanks Jonathan for help.

	Now I want to have the \discretionary command to allow glue in its pre-, post-, etc, parameters. I've read the XeTeX document generated from .WEB file. I think just by modifying the following modules: <Display discretionay p>, <Compute the discretionary break width values>, <Subtract the width of node v from break width>, <Try to break after a discretionary fragment, then ...>, and the <Transplant the post-break list>, <Transplant the pre-break list> and have them to allow glue node, I can expand the TeX part of \discretionary to allow glues. But I can't figure out if it interferes with XeTeX implementation. And if I want \discretionary support UTF16 chars directly instead of \char"FE3D like stuff, is there anything else I should do?

	Any comment about that?

Regards!
Lobsang Sonam