Using ANY Stix Two Math OTF character in text and math modes without loading it as math font

Question

First a little background. I am using MathTime Pro II (which is not an OpenType Font) as my math font and do not want to replace it. I think this precludes my loading unicode-math if I want to use the OTF versions of all other fonts. I am successfully using the OTF versions of TeX Gyre Termes for Roman, TeX Gyre Heros for sans serif, and Microsoft's Consolas for typewriter. Obviously, I am compiling with XeTeX and using fontspec but not unicode-math.

Now to the specifics of my question(s) (which was difficult to condense into the question title). I have figured out how to access individual characters from the OTF version of Stix Two Math using, for instance, {{fontspec{STIX Two Math}\char"27D3}}, although I am not sure this will work in math mode (I am using that particular character as a type of QED symbol and it is in text mode). So my first question is:

• Will this work in math mode? If not, what alteration do I need to make to get this to work in math mode?

I have not figured out how to access characters with codes above FFFF. The errors I was getting led me to Bad Character Code Error in Math Mode for Unicode Character, where I thought I had found the answer; despite numerous attempts, I have been unable to wrestle that code into a form that solves my problem. So my second question is:

• How can I access characters with codes above FFFF in the Stix Two Math OTF font (or any font, for that matter)?

I realize this is a multifaceted question but was afraid breaking it up into two questions would obfuscate the answer. I hope I have successfully provided the setting and what I am trying to accomplish. Ultimately, I want the entire Stix Two Math OTF font available to me without having to replace MathTime Pro II. I will likely only need a few characters at a time.

Answer 1

You haven't shown what you did, or what error you got.

This shows stix two math alongside latin modern tfm fonts, mathtime would be the same.

\documentclass{article}
\usepackage{fontspec}
\newfontface\StixTwoMath{STIXTwoMath-Regular.otf}[NFSSFamily=stixtwomath,Script=Math]
\DeclareSymbolFont{stixtwomath}{TU}{stixtwomath}{m}{n}
\Umathchardef\myA "0 \symstixtwomath "1D400
\begin{document}
{\StixTwoMath \char"1D400 / }
[ \myA \neq A ]
\end{document}

Answer 2

Here is a math-mode \stixtwosymbol command (based on \boldsymbol from amsbsy) that replaces any arbitrary symbol with the one from STIX Two Math. it also creates a \mathversion{stixtwo} and a \stixtwomath, which work just like \mathversion{bold} and \boldmath.

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{New Computer Modern Math Book}
\setmathfont{STIX Two Math}[version=stixtwo]
\makeatletter
\newcommand\stixtwomath{\mathversion{stixtwo}}
%% Based on the definition of \boldsymbol from amsbsy.sty"
\DeclareRobustCommand{\stixtwosymbol}[1]{%
  \begingroup%
  \let@nomath@gobble \mathversion{stixtwo}%
  \math@atom{#1}{%
  \mathchoice%
    {\hbox{$\m@th\displaystyle#1$}}%
    {\hbox{$\m@th\textstyle#1$}}%
    {\hbox{$\m@th\scriptstyle#1$}}%
    {\hbox{$\m@th\scriptscriptstyle#1$}}}%
  \endgroup}
\makeatother
\begin{document}
\noindent( x \triangleright y )\
( x \stixtwosymbol{\triangleright} y)
\end{document}

You could instead use any arbitrary text-mode command, including setting the font family followed by \symbol{"123A}, by wrapping it in \text from amsmath (or amstext). If you need it to have any spacing other than \mathord, you need to wrap it again in the math class, such as,

\newfontface\symbolfont{STIX Two Math}
\newcommand\triangleright{\mathbin{\text{\symbolfont\symbol{"2A65}}}}

However, a frame challenge: if what you really want is to use certain symbols from a different math font, consistently, use the range= option from unicode-math:

\defaultfontfeatures{Scale=MatchLowercase}
\setmathfont{New Computer Modern Math Book} % Or your font of choice
\setmathfont{STIX Two Math}[range={\triangleleft,\triangleright}]

You can also set ranges and alphabets, and use hex or decimal Unicode codepoints instead of symbolic names. So, for example

\setmathfont{STIX Two Math}[StylisticSet=8, range={"222B-"2233,"2A0B-"2A1C}]

changes all the integrals to upright, or

\setmathfont{STIX Two Math}[StylisticSet=1, range={scr, bfscr}]

changes the \mathscr and \mathbfscr alphabets from a copy of \mathcal to a script font.