How to get \backprime if the main math font is Cambria Math?

Question

Running xelatex on

\documentclass{standalone}
\usepackage{unicode-math}
\setmathfont{CambriaMath.ttf}
%\setmathfont[Ligatures=TeX,range={\backprime}]{TeX Gyre Termes Math}
%\setmathfont[Ligatures=TeX,range={"2035}]{TeX Gyre Termes Math}
%\setmathfont[Ligatures=TeX,range={"02035}]{TeX Gyre Termes Math}
%\setmathfont[range={\backprime}]{texgyretermes-math.otf}
%\setmathfont[range={"2035}]{texgyretermes-math.otf}
%\setmathfont[range={"02035}]{texgyretermes-math.otf}
\begin{document}
\(\sigma^{\backprime}\)
\end{document}

with both CambriaMath.ttf and texgyretermes-math.otf in the working directory results in

As the reader sees above, I undertook several attempts of using \setmathfont; none of them works for me. lualatex produces a no better result.

How to get the reverse prime (as the right superscript) when using Cambria Math as the main math font? Of course, I'd also like to get proper copyable Unicode σ‵ (or similar for the backprime) in the text layer of PDF produced.

Versions used:

• This is XeTeX, Version 3.14159265-2.6-0.99999 (TeX Live 2019/dev/Debian) (preloaded format=xelatex 2019.4.18)

• LaTeX2e <2018-12-01>

• Document Class: standalone 2018/03/26 v1.3a Class to compile TeX sub-files standalone

• Package: unicode-math 2019/02/15 v0.8n Unicode maths in XeLaTeX and LuaLaTeX

• Cambria Math versions 5.96 or 6.96 (the only difference wrt. issue is that the missing-symbol image looks differently).

Crosspost: http://github.com/wspr/unicode-math/issues/529

Answer 1

One side note: on many systems, Cambria Math will be in the file cambria_01.ttf or cambria.ttc. Therefore, the only portable way to select it is by its display name. That’s not the cause of your error, but it’s something I needed to change to get your MWE to compile.

It’s a bug in unicode-math that range=\backtick and range="2035 don’t work. As of August 2019, \DeclareMathSymbol does not work either. Here is a workaround, based on this answer.

\documentclass{standalone}
\usepackage{unicode-math}

\defaultfontfeatures{Scale=MatchLowercase}

\setmathfont{Cambria Math}

\newfontface\STIXTwoMath{STIX Two Math}[NFSSFamily=STIXTwoFamily]
\DeclareSymbolFont{Missing}{TU}{STIXTwoFamily}{m}{n}
\Umathchardef\varbackprime="0 \symMissing "2035

\newcommand\textbackprime{{\STIXTwoMath\symbol{"2035}}}

\begin{document}
\(\sigma^{\varbackprime}\)
\end{document}

This has more space to the sides of the tick than you might want.

A simpler approach is to use \text from amsmath to display the symbol from text mode. à la \textbackprime above.