\starttext

\bgroup
\unexpanded\def\ {\mathortext\normalspaceprimitive\space}
x. x, x.\ x,\ x \par
x. x, x.\space x,\ x \par
\let\ = \normalspaceprimitive x. x, x.\ x,\ x \par
\egroup

\bgroup
\unexpanded\def\ {\mathortext\normalspaceprimitive\space}
x. x \par
x.\ x \par
x.\space x \par
\let\ = \normalspaceprimitive x.\ x \par
\egroup

\stoptext
