%%
%% The LaTeX Companion, 3ed
%%
%% Example 4-1-33 on page I-279 in "Styling description-like lists".
%%
%% 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{147.0pt}
%StartShownPreambleCommands
 \usepackage{enumitem}
%StopShownPreambleCommands

\begin{document}
 \begin{description}[style=sameline]
 \item[X]  Compare this text with that from the
           previous example.
 \end{description}
 \begin{description}[style=nextline]
 \item[Medium]          This text starts on a new line.
 \item[A fairly long label --- so what happens now?]
     It breaks and the item text starts on a new line.
 \end{description}
\end{document}