%%
%% The LaTeX Companion, 3ed
%%
%% Example 7-4-9 on page I-552 in "subcaption --- Substructuring floats".
%%
%% 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{165.0pt}

%StartShownPreambleCommands
\usepackage{graphicx,subcaption}
%StopShownPreambleCommands

\begin{document}
\begin{figure} \centering
  \subcaptionbox
      {Small, but a large caption\label{sf1}}[2cm]
      {\includegraphics[width=12mm]{elephant}}
  \qquad
  \subcaptionbox{Bigger\label{sf2}}
      {\includegraphics[width=18mm]{elephant}}
  \caption{Two elephants}\label{elephants}
\end{figure}
Figure~\ref{elephants} contains subfigure~\ref{sf1},
which is smaller than subfigure~\ref{sf2}.
\end{document}