iftx@ch 是什么意思（以 newtx 为单位）？

Question

我买了一台新的 win10 电脑，安装 XeLaTeX 东西时遇到了麻烦。编译器在 untxmia.fd 处给出错误。

我猜这意味着我忘记安装一些字体/软件包。但我不明白这是什么iftx@ch意思。

平均能量损失

\documentclass[12pt,a4paper,openany,fleqn]{book}
\usepackage[margin=2cm, top=2cm]{geometry}
\renewcommand{\rmdefault}{ptm}
\usepackage{amsmath}

\usepackage[no-math]{fontspec}


\usepackage{xeCJK}
\setmainfont{Times New Roman Bold}
\usepackage[subscriptcorrection,nofontinfo,zswash,mtphrb]{mtpro2}



\defaultfontfeatures{Ligatures=TeX} 
\setCJKmainfont[ItalicFont={新細明體},BoldFont={新細明體}]{新細明體} 
\XeTeXlinebreaklocale "zh"
\XeTeXlinebreakskip = 0pt plus 1pt


\newfontfamily\schola{Times New Roman}


\makeatletter
\newif\iftx@libertine
\newif\iftx@minion
\newif\iftx@coch
\makeatother

\DeclareSymbolFont{lettersffA}{U}{ntxmia}{m}{it}
\SetSymbolFont{lettersffA}{bold}{U}{ntxmia}{b}{it}
\DeclareMathSymbol{+}{\mathbin}{lettersffA}{253}

\DeclareSymbolFont{vvsymbols}{OMS}{txsy}{m}{n} %OMS, txsy works
\SetSymbolFont{vvsymbols}{bold}{OMS}{txsy}{bb}{n}

\DeclareMathSymbol{\times}{\mathbin}{vvsymbols}{2}
\DeclareMathSymbol{-}{\mathbin}{vvsymbols}{0}



\begin{document}
$123$
\end{document}

的代码untxmia.fd如下

%Filename: untxmia.fd
%Created by: tex mia-drv
%Created using fontinst v1.933

%THIS FILE SHOULD BE PUT IN A TEX INPUTS DIRECTORY

\ProvidesFile{untxmia.fd}
   [2018/04/14 Fontinst v1.933 font definitions for U/ntxmia.]

\expandafter\ifx\csname ntxmath@scaled\endcsname\relax
  \let\ntxmath@scaled\@empty%
\fi

\DeclareFontFamily{U}{ntxmia}{\skewchar \font =127}

\iftx@libertine
  \DeclareFontShape{U}{ntxmia}{m}{it}{
     <-> \ntxmath@scaled nxlmia
  }{}

  \DeclareFontShape{U}{ntxmia}{b}{it}{
     <-> \ntxmath@scaled nxlbmia
  }{}
\else
  \iftx@minion
    \DeclareFontShape{U}{ntxmia}{m}{it}{
      <-> \ntxmath@scaled zmnmia
    }{}

    \DeclareFontShape{U}{ntxmia}{b}{it}{
      <-> \ntxmath@scaled zmnbmia
    }{}
  \else
    \iftx@coch
      \DeclareFontShape{U}{ntxmia}{m}{it}{
        <-> \ntxmath@scaled zcochmia
      }{}
      \DeclareFontShape{U}{ntxmia}{b}{it}{
        <-> \ntxmath@scaled zcochbmia
      }{}
    \else
        \iftx@ch
          \DeclareFontShape{U}{ntxmia}{m}{it}{
            <-> \ntxmath@scaled zchmia
          }{}
          \DeclareFontShape{U}{ntxmia}{b}{it}{
            <-> \ntxmath@scaled zchbmia
          }{}
        \else
          \iftx@stxtwo
            \DeclareFontShape{U}{ntxmia}{m}{it}{
              <-> \ntxmath@scaled ntxstx2mia
            }{}
            \DeclareFontShape{U}{ntxmia}{b}{it}{
              <-> \ntxmath@scaled ntxstx2bmia
            }{}

          \else
            \DeclareFontShape{U}{ntxmia}{m}{it}{
              <-> \ntxmath@scaled ntxmia
            }{}
            \DeclareFontShape{U}{ntxmia}{b}{it}{
              <-> \ntxmath@scaled ntxbmia
            }{}
          \fi
        \fi
    \fi
  \fi
\fi
\DeclareFontShape{U}{ntxmia}{m}{sl}{<->ssub * ntxmia/m/it}{}
\DeclareFontShape{U}{ntxmia}{bx}{it}{<->ssub * ntxmia/b/it}{}
\DeclareFontShape{U}{ntxmia}{b}{sl}{<->ssub * ntxmia/b/it}{}
\DeclareFontShape{U}{ntxmia}{bx}{sl}{<->ssub * ntxmia/b/sl}{}

\endinput