%%
%% The LaTeX Companion, 3ed
%%
%% Example 2-2-8 on page I-41 in "The basic interface".
%%
%% 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{159.0pt}
%StartShownPreambleCommands
\usepackage[sf,bf,tiny,center]{titlesec}
\titlelabel{\thetitle.\enspace}
%StopShownPreambleCommands

\begin{document}
\section{A section}
\subsection{A subsection}
\subsubsection{A subsubsection}
Three headings following each other, a situation you
will not see very often \ldots
\end{document}