[XeTeX] Single glyphs from a font

[Joel C. Salomon]

Ross Moore wrote:
> On 09/06/2009, at 6:08 AM, Joel C. Salomon wrote:
>>> I’m trying to create this effect:
>>>     a² + b² = c²   (1)
>>>     x² + y² = z²   (1′)
>>
>> I think I figured it out.  In my preamble I have:
>>     \newfontface\cambriamath{Cambria Math}
>>     \newcommand{\textprime}{\cambriamath ′}
>> Then the equation looks like:
>>     \begin{equation} \label{abc}
>>        a^2 + b^2 = c^2
>>     \end{equation}
>>     \begin{equation*} \label{abc:prime} \tag{\ref*{abc}\textprime}
>>        x^2 + y^2 = z^2
>>     \end{equation*}
>> This works, but need I be wary of font-change commands in \tag{}s?
>
> Yes, you probably should be.
<snip>
> Now to get the math symbol using Cambria, do similarly
> to my previous posting about \ldots and \cdots, etc.
>  (on the  "Unicode maths for TeX"  email list)
> viz.
>
> \makeatletter
>     \let\UnicodeMathSymbol\um at mathsymbol@noparse
>     \UnicodeMathSymbol{"02026}{\mathellipsis}{\mathrel}{ellipsis}%
>     \UnicodeMathSymbol{"02032}{\prime}{\mathord}{prime}%

OK, we’re filling what’s missing from unicode-math.tex.  I tried that,
but I missed the
    \let\UnicodeMathSymbol\um at mathsymbol@noparse
that makes the command work!

>     \let\prime ′
>     \let\mathellipsis …

Noting for the record that defining \mathellipsis causes amsmath’s
\dotsc &c. to use that symbol.  (You know that, but I only found that
out by searching my MiKTeX installation tree.)

>     \let\@ldots …
>     \let\@cdots ⋯
> \makeatother

What are these definitions for?  These commands are about to be
unaccessible after \makeatother.  Is there some package that’s expecting
these names?

(B.T.W., unicode-math.tex already declares ‘⋯’ to be a \mathrel, so I
omitted that line.)

So basically, the reason \tag{\ref*{abc}$′$} didn’t work before was that
the TeX didn’t know what math category the prime character fell into, so
it got ignored?

> Now even this works:    \tag{$\ref{abc}'$}
> using the ordinary ASCII single-quote/apostrophe.
Not quite; $'$ has some superscripting magic associated with it.  Try
$\prime{}'$ and you’ll see the difference.  (Without the ‘{}’, you’ll
get a weird primed prime.)

(B.T.W., re. the ‘*’:  I’m using hyperref; Ignore it.)

Thanks for the help,
—Joel Salomon