%%
%% The LaTeX Companion, 3ed
%%
%% Example A-1-16 on page II-644 in "Using argument processors".
%%
%% 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{135.0pt}
%StartShownPreambleCommands
\NewDocumentCommand\withspace{m}{\textbf{#1}}
\NewDocumentCommand\spaceless{>{\TrimSpaces}m}{\textbf{#1}}
%StopShownPreambleCommands

\begin{document}
Test \withspace{ Hello world }  lighten up!        \par
Test \spaceless{ Hello world } lighten  up!
\end{document}