[XeTeX] Whitespace in input

[Philip and Le Khanh]

Keith J. Schultz wrote:

> A non.breaking space is to me a printable character, in so far that
> it is important and must be used to distinguish between word space, et all.

If, for you, "[a] non.breaking space is a printable character", then
presumably that character must be taken from some font.  If you take
a character from a font, it will have a size, and although it can be
combined with kerning rules to adjust its position w.r.t. adjacent
characters,  the logic for this is fairly restricted.  In particular,
it cannot take into account the amount by which TeX is seeking to
expand or contract spaces on the current line in order to achieve
optimal paragraphs.  So in your model of the ideal universe, 
non-breaking Unicode spaces would not behave as do conventional
TeX non-breaking spaces (which /do/ expand and contract to assist
in TeX's line-breaking), nor would they conform to their Unicode
definition where their decomposition is defined as :

	<noBreak> SPACE (U+0020)

I wonder if you would like to discuss these points ?

Philip Taylor