How can I use ucharclasses to change the font for a special script and then restore to what it was before?

Question

I would like to change the font in XeLaTeX when I enter a new Unicode block with a certain Script (e.g. Devanagari for Hindi languages). The ucharclasses package seems to do exactly that.

However, when I leave the place where the different script is used and go back to what I had before (e.g. latin script) I loose the formatting (e.g. boldface) and the font size.

To illustrate, try this:

\documentclass[10pt,a5paper,DIV12,BCOR8.25mm,twoside,parskip=half]{scrreprt}

\usepackage[Devanagari]{ucharclasses}
\usepackage{xltxtra}
\usepackage{fontspec}
\setmainfont[Mapping=tex-text]{Liberation Serif}
\setsansfont[Mapping=tex-text]{Liberation Sans}
\setmonofont[Mapping=tex-text]{Liberation Mono}
\newfontfamily\hindifont{Siddhanta}
\setTransitionsFor{Devanagari}{\hindifont}{\rm}


\begin{document}
\tableofcontents
\section{A latin script section}
Some latin script
\section{Devanagari: ताजा धनिया के साथ अनायास and so on}
A mixture \textbf{ of normal text and ताजा धनिया के साथ अनायास Devanagari script} in bold
\section{Some more latin script}
Some latin script
\end{document}

The output looks like this:

The \setTransitionTo correctly picks up the Devanagari script and changes the font to Siddhanta. However, when I come back to latin script, the boldface is gone and the fontsize is increased. The table of contents line shows the same problem.

N.B. \setTransitionsFor{...}{...}{...} is what the documentation describes as \setTransitions. The doc seems to be wrong.

Answer 1

You can try something like this (I used the ^^-notation because I don't have an utf8-editor here):

\documentclass[10pt,a5paper,DIV12,BCOR8.25mm,twoside,parskip=half]{scrreprt}
\usepackage[Devanagari]{ucharclasses}
\usepackage{fontspec}

\newfontfamily\hindifont{Arial Unicode MS}
\makeatletter
\setTransitionsFor{Devanagari}%
 {\let\curfamily\f@family\let\curshape\f@shape\let\curseries\f@series\hindifont}
 {\fontfamily{\curfamily}\fontshape{\curshape}\fontseries{\curseries}\selectfont}
\makeatother

\begin{document} \tableofcontents \section{A latin script section} Some latin script

\section{Devanagari: ^^^^0908 ^^^^0909 and so on} A mixture \textbf{ of normal text and ^^^^0908 ^^^^0909 Devanagari script} in bold
\section{Some more latin script} Some latin script

\end{document}

Answer 2

I think it's easy:

\def\ResetTransitionTo#1{%
  \XeTeXinterchartoks 255 \csname#1Class\endcsname{\relax}}
\setTransitionsFor{Devanagari}
  {\begingroup\ResetTransitionTo{Devanagari}\sethindifont}
  {\endgroup}

This is what we do in xeCJK. Note that we must reset the \XeTeXinterchartoks to make the group balance. It is a place that ucharclasses is not very well implemented.

Hmm, spaces between scripts are necessary here. It's very boring to define all transitions for all scripts in the document, if there are many.