[XeTeX] Glue between ideographs suggested

[Yin Dian]

Hi all,

  I'm a Chinese LaTeX user and new to XeTeX. It greatly attracts me that I
can use nearly all fonts installed in my system with little configuration
and I can even use macros like \@tfor to iterate over Chinese character
sequences, which I could hardly imagine using TeX/LaTeX. However, IMO XeTeX
is still not ready for practical use for typesetting Chinese documents. One
serious problem is that there should be a way to insert glue between Chinese
characters, while de facto not AFAIK. Without glues between Chinese
characters it's quite easy to have overfull or underfull boxes in a line,
even if I have used macro to adjust kerning and hskip of the fullwidth
punctuations, as you can see in the attachment. The case is that when a line
contains no punctuations or just come along with punctuation prohibitions,
the line is likely to be overfull or underfull. The solution is to insert
intercharacter glues, just as LaTeX CJK does to insert \CJKglue, or pTeX ( a
Japanese variant of TeX) to insert \kanjiskip. Without this mechanism it's
hard to typeset a fine-looking Chinese or Japanese article.

  So the problem is how we could implement this. Making all ideographs
active and redefine them is obviously a bad idea, not to mention that there
are nearly seventy thousand ideograms defined in Unicode 4.0. Preprocessing
is possible, but is likely to break down the prohibitions, and writing an
accurate and contextual preprocessor is quite a tough job. I don't know
whether there is a way to implement this using macros, or we should add this
support in the XeTeX source code. Maybe we should take a look at other
Unicode-based TeX variants to see how they handle this, such as
Omega/Lambda, which I know little about. This needs careful consideration
and discussion.

  For example, suppose there is a \CJKglue inserted between ideographs, then
how could we handle it? One may want to add an underline or underwave to a
sequence of ideograms and allow linebreak between them, just like that in
CJKulem.sty and CJKfntef.sty, in which way we should apply the underline to
the glues; one may also want to add a separate underline beneath each
character inconsecutively, in which way we should skip the glues and only
apply the underline to the ideographs. Also one may want to disable the
insertion of glues, or enable it. How to handle the glue is also a big
problem. I know little about other typesetting systems, so I post the
question here and long for your discussions and suggestions on how to insert
glues between ideographs, as I think XeTeX is a most powerful and promising
TeX variant.

  Best regards!

Dian YIN (尹甸)
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