<..latex ltspace..>
\NewConfigure{hspace}{3}
\Configure{hspace}{}{}{ }
\def\:temp#1{\tmp:dim=#1\relax
\a:hspace \hsp:c\hskip #1\relax\b:hspace}
\HLet\@hspace=\:temp
\def\:temp#1{\tmp:dim=#1\relax
\a:hspace \hsp:c\vrule \@width\z@\nobreak
\hskip #1\hskip \z@skip\b:hspace}
\HLet\@hspacer=\:temp
\def\hsp:c{\ifdim \tmp:dim<1em\else\c:hspace\fi
\ifdim \tmp:dim<2em\else\c:hspace\fi
\ifdim \tmp:dim<3em\else\c:hspace\fi
\ifdim \tmp:dim<4em\else\c:hspace\fi
\ifdim \tmp:dim<5em\else\c:hspace\fi}
-_-_-
We need the assignment to \tmp:dim because of commands like \hspace{0.25em plus 0.125em minus 0.08em}.
<..latex ltspace..>+
\let\:tempc\@vspace
\append:defI\:tempc{\a:vspace{#1}}
\HLet\@vspace\:tempc
\let\:tempc\@vspacer
\append:defI\:tempc{\a:vspace{#1}}
\HLet\@vspacer\:tempc
\NewConfigure{vspace}[1]{\def\a:vspace##1{#1}}
\Configure{vspace}{}
-_-_-