%%
%% The LaTeX Companion, 3ed
%%
%% Example 7-4-13 on page I-554 in "Customizing the subcaptions".
%%
%% 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}


  \setlength\intextsep{8pt}  % less space between here floats in the example

%StartShownPreambleCommands
\usepackage[font=sf]{caption}  \usepackage{subcaption}
\newcommand\FIG{\fbox{\parbox{.4\textwidth}{\strut}}}
\newcommand\samplefig[1]{\begin{figure}[ht]
 \centering
 \subcaptionbox{Short caption}{\FIG}
 \subcaptionbox{A longer caption with more text}{\FIG}
 \caption{#1}\end{figure}}
%StopShownPreambleCommands

\begin{document}
\samplefig{Default subfigures}
\captionsetup[sub]{font=footnotesize,textfont={rm,it},
  labelfont={rm,bf},labelformat=simple,
  labelsep=period,format=hang,margin=5pt,
  justification=raggedright,position=top}
\samplefig{Customized subfigures}
\end{document}