%%
%% The LaTeX Companion, 3ed
%%
%% Example 9-3-6 on page I-665 in "Standard font shapes".
%%
%% 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{147.0pt}

  \setlength\parindent{0pt}

%StartShownPreambleCommands
\usepackage{tgpagella,color}
\newcommand\testnesting[1]{#1.\ \emph{First \emph{second
    \emph{third \emph{fourth \emph{fifth}}}}}\par}
%StopShownPreambleCommands

\begin{document}
\testnesting{1a}               \textit{\testnesting{1b}}
\DeclareEmphSequence{\itshape,\upshape\scshape,\itshape}
\testnesting{2a}               \textit{\testnesting{2b}}
\DeclareEmphSequence{\itshape,\color{blue},\bfseries,
  \normalcolor\scshape}                 \testnesting{3a}
\DeclareEmphSequence{\itshape,\emforce\color{blue},
  \bfseries,\color{black}\scshape}      \testnesting{3b}
\end{document}