%%
%% The LaTeX Companion, 3ed
%%
%% Example A-1-12 on page II-637 in "Creating document commands and environments".
%%
%% 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{207.0pt}
\newcounter{Citctr}
\NewDocumentEnvironment{Citation}{ m }
   {\stepcounter{Citctr}\begin{description}
      \item[Citation \arabic{Citctr}]}
   {\hspace*{\fill}\nolinebreak[1]%
    \quad\hspace*{\fill}%
    \finalhyphendemerits=0
    \emph{#1}\end{description}}
%StartShownPreambleCommands

%StopShownPreambleCommands

\begin{document}
\begin{Citation}{Protagoras} Man is the
 measure of all things.     \end{Citation}
\begin{Citation}{Blaise Pascal}
 On mourra seul.            \end{Citation}
\begin{Citation}{William Pitt} Necessity
 is the plea for every infringement of
 human freedom.             \end{Citation}
\end{document}