%%
%% The LaTeX Companion, 3ed
%%
%% Example 3-3-6 on page I-158 in "Indefinite forms".
%%
%% 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\parindent{0pt}
%StartShownPreambleCommands
\usepackage{acro}
\DeclareAcronym{ufo}{short=UFO\@, long=unidentified
    flying object, long-indefinite = an}
%StopShownPreambleCommands

\begin{document}
1 \Iac{ufo}, 2 \iac{ufo}, 3 \iacl{ufo}, 4 \iacs{ufo},
5 \iacf{ufo}
\end{document}
