%     Test file to see what is inside an \halign
\tracingonline=1
\tracingmacros=2
\tracingcommands=2
\showboxbreadth=255
\showboxdepth=255
\newbox\q
\setbox\q=\vbox{\halign{#\hfil&\quad#\hfil\cr
foo & bar \cr
\noalign{\vbox{quux}}
Longer foo & longer bar \cr
steeple \cr
& chase \cr}}
%\vbox{\unvbox\q\global\setbox\q=\lastbox}
%\showbox\q

\long\def\try#1{The following was passed as param 1:

#1

That's that.  Here's what's left:\par}

\vbox{\try{\unvbox\q}}