[XeTeX] unicode-math package and \UnicodeMathSymbol command

[Joel C. Salomon]

Ross Moore wrote:
> ... in doing this, you are going *against* standard (and TeX) usage.
> In the TeXBook (p.134) it is clear that  \colon  is meant to be
> punctuation, and  :  is meant to have relation spacing in math.
<snip>
> Indeed I think that it is wrong to have this
> in  unicode-math-add.tex :
> 
>    \UnicodeMathSymbol{"0003A}{\colon}{\mathpunct}{}%
> 
> especially so since  unicode-math.tex  already has this:
> 
>    \UnicodeMathSymbol{"02236}{\colon}{\mathrel}{ratio}
> 
> which follows AMS usage, but which differs from the original \TeX .
> 
> It is most unfortunate that, over the years, there has been
> a lot of confusion about the use of  \colon  and  : .
> It's not at all clear how this should be sorted out now.
> Probably it depends upon what font designers have chosen to do.

This is an issue Will knows about; see the GitHub bug tracker at
<http://github.com/wspr/unicode-math/issues/#issue/7>.  It’s the Unicode
folks, not font designers, that have decided the issue (somewhat): ‘:’
[U+003A] is called “Colon”, the punctuation mark, while ‘∶’ [U+2236] is
the “Ratio” relation symbol.

BTW, I’m not sure what you mean by AMS usage differing from the original
TeX; both the “Short Math Guide” and the amsmath package documentation
say that ‘:’ has relation spacing and ‘\colon’ is for punctuation, /à
la/ the TeXBook.

It seems that, somewhat counter-intuitively, ‘:’ [U+003A] ought to be a
synonym for the mathrel ‘∶’ [U+2236], and ‘\colon’ must be used to
include the actual [U+003A] mathpunct.

—Joel Salomon