%%
%% The LaTeX Companion, 3ed
%%
%% Example 4-2-12 on page I-305 in "Customization keys for typesetting".
%%
%% 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{183.0pt}

%StartShownPreambleCommands
\usepackage{fancyvrb} \usepackage[T1,OT1]{fontenc}
%StopShownPreambleCommands

\begin{document}
\fontencoding{OT1}\selectfont \hrule
\begin{Verbatim}[fontfamily=tt]
  `tt' is fine in OT1: \sum_{i=1}^n
  UTF-8 char test: äöüß œ Æ $ £
\end{Verbatim}
\begin{Verbatim}[fontfamily=helvetica]
  But `helvetica' fails in OT1: \sum_{i=1}^n
  UTF-8 char test: äöüß œ Æ $ £
\end{Verbatim}
\fontencoding{T1}\selectfont \hrule
\begin{Verbatim*}[fontfamily=helvetica]
  ...  while it works in T1: \sum_{i=1}^n
  UTF-8 char test: äöüß œ Æ $ £  »„«
\end{Verbatim*}
\end{document}