[XeTeX] unicode-math package and \UnicodeMathSymbol command

[Joel C. Salomon]

Joel C. Salomon wrote:
> Ross Moore wrote:
>> 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>.

…and, of course, Ross Moore knows all about this too.  Just found a
thread from four years back about this very issue:
<http://www.tug.org/pipermail/xetex/2005-July/002374.html>.

> 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.

And now that I found that thread, especially the post at
<http://www.tug.org/pipermail/xetex/2005-July/002390.html> where Will
points out all the slightly-incompatible definitions of ‘:’ and
‘\colon’, I’m even more confused than before.  Except I think I need to
revise my last paragraph:

> 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.

Since there are already so many different ways ‘:’ and ‘\colon’ are
defined, I think it might be safe to have ‘:’ [U+003A] be mathpunct, ‘∶’
[U+2236] be mathrel, ‘\colon’ map to the more difficult-to-type ‘∶’
[U+2236], and just let the incompatibility be.

—Joel Salomon