%%
%% The LaTeX Companion, 3ed
%%
%% Example 4-3-15 on page I-343 in "paracol --- Several text streams aligned".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{141.0pt}

%StartShownPreambleCommands
\usepackage{paracol}
\definecolumnpreamble{0}{\bfseries}    % \upshape missing
\definecolumnpreamble{1}{\mdseries\itshape}
%StopShownPreambleCommands

\begin{document}
\begin{paracol}{2}
  body text \switchcolumn  Mengentext    \switchcolumn*
  em-dash   \switchcolumn  Geviertstrich
\end{paracol}
\end{document}