[XeTeX] [unimath] Re: Should xelatex have its own kernel? (was: "Conflict between xunicode and fontspec?")

[Joel C. Salomon]

On Feb 7, 2008 7:06 PM, Will Robertson <wspr81 at gmail.com> wrote:
<Re. U+2007 Figure Space>
>
> Without knowing the reasoning behind this glyph, I'll go out on a limb
> and predict that this space character is designed to be used in
> tabular material with fixed-width numbers, when a usual space wouldn't
> necessarily be the right width for the text to align vertically
> between lines.

Correct; from <http://fileformat.info/info/unicode/char/2007>:
> space equal to tabular width of a font
> this is equivalent to the digit width of fonts with fixed-width digits

> > Indeed, should XeTeX be smart enough to *insert* these
> > spacing characters into the output that it creates?
> > This is particularly relevant to the typesetting of
> > mathematics, and it would indeed be a departure from
> > the way TeX currently works.
>
> I think we can safely assume that the TeX community knows more about
> mathematical typesetting than any font designer (with a couple
> exceptions). Therefore I'd say it's reasonable not to use the unicode
> characters for these spaces when PDF is the output mode. Most fonts
> don't even have most of the characters, right?

I've been favorably impressed by Murray Sargent's "Nearly Plain-Text
Encoding of Mathematics" (http://unicode.org/notes/tn28/); perhaps the
copy-and-pasteable text in the PDF file should be (mostly) compatible
with that.

Oh, and the space characters are *not* present in the utn28 encoding.
They are used only to select the spacing around operators &c.

(I could be wrong about all this, of course, but that's my reading of
Murray's paper.  Will, you want to ask him directly?)

> > Against this is the question of how do "smart" math fonts
> > handle the spacing? (e.g. the STIX fonts).
>
> I don't believe there is any font that smart yet.
> Although I don't think it's impossible... But what font designer would
> bother, when you need a typesetting program to do at least some of the
> work for you?

*Some* of the spacing options are set in a good maths font.
(Generalizing from -- what, three? instances.)

> I mean, you could approximate good maths typesetting with plain
> unicode text with all these spaces and so on, but you'd still not be
> able to do superscripts or subscripts, or limits, or integrals that
> change size, or square roots, or ... so what's the point?

Doesn't Cambria Math include different glyphs for subscript and
scriptscript sizes, and for constructing integrals and radicals of
different heights?  But for copy-and-paste, they should be encoded as
'∫' or '√'.

--Joel