I'm trying to modify a package to suit my needs but since I'm not very familar with the tex macro language I would like to add a border around the boxes created by the package so I can see exactly what they are doing.
The code that allocates the boxes is
\setbox0\box\csname pc@column@\number\count@\endcsname%
\csname pc@column@width@\number\count@\endcsname\z@%
\vbox{\unvbox\@tempboxa}%
and I'd like to simply put a frame around it or even give it a unique semi-opaque background color.
\setbox0\hbox{...}to\setbox0\hbox{\fbox{...}}and that puts rules around the box but if the usage is as you show with\unvboxthen the extra fbox box will prevent the contents being unboxed and the package will fail to work. If you put colour in and the code tries to use \lastbox then the colour special will hide the box and \lastbox will be null. That is why people request MWE the question (especially this one) are not answerable otherwise. – David Carlisle May 11 '12 at 14:04