Plain Tex defines \quad
so:
\def\quad{\hskip1em\relax}
Why is the \relax
there? It's usually used as a token that can't be expanded, serving as a "do nothing" operation after macro expansion is finished. But that use seems redundant, because it follows a command, namely \hskip
.
The macro is defined alongside \enskip
and \qquad
in plain.tex, and in Latex in ltspace.dtx
.
An idle question, but I guess the reason for it will be worth knowing.