% line 6 testex.mp
TeX \hsize="a0 inmore TeX  % with comments%
\shipout\hbox{\smash{\hbox{\hbox{% line 10 testex.mp
$a+b$}\vrule width1sp}}}
\shipout\hbox{\smash{\hbox{\hbox{% line 10 testex.mp
An initial newline is now ignored.}\vrule width1sp}}}
\end{document}