%%
%% The LaTeX Companion, 3ed
%%
%% Example 2-3-15 on page I-74 in "Typesetting a contents list".
%%
%% 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{135.0pt}
%StartShownPreambleCommands
\makeatletter
\renewcommand\l@subsection{\@dottedtocline{2}{1.5em}{3em}}
\makeatother
%StopShownPreambleCommands

\begin{document}
\contentsline{section}{\numberline{10}A-Head}{3}{}%
\ldots % several more heading lines here
\contentsline{subsection}{\numberline{10.9}B-Head}{7}{}%
\contentsline{subsection}{\numberline{10.10}B-Head}{8}{}%
\end{document}