\catcode`@=11

\def\basevskip{\par\ifdim\prevdepth>\z@\vskip-\prevdepth\fi
  \begingroup\afterassignment\bas@vskip\skip@=}
\def\bas@vskip{\vskip\skip@\endgroup\prevdepth\z@}

\catcode`@=12

\def\visualbox#1#2#3{%
  \hbox{%
    \vrule height#2depth#3\hskip-0.4pt%
    \vbox{%
      \hrule width#1\vskip-0.4pt%
      \vskip#2%
      \vskip-0.4pt\hrule
      \vskip#3%
      \vskip-0.4pt\hrule
      \vskip-#3%
    }%
    \hskip-0.4pt\vrule height#2depth#3%
  }%
}

\def\myboxesa#1{%
  \visualbox{10mm}{12mm}{4mm}%
  #1%
  \visualbox{8mm}{10mm}{2mm}%
}

\def\myboxesb#1{%
  \visualbox{10mm}{12mm}{4mm}%
  #1%
  \visualbox{8mm}{4mm}{2mm}%
}

\font\eighttt cmtt10 at8pt

\def\stringize#1{\string#1\thinspace}

\def\myvboxes#1#2#3#4{%
\vbox to34mm{%
  \baselineskip#1\lineskip#2\lineskiplimit#3%
  \hbox{\vtop{\myboxesa{#4}}\hskip1mm\vtop{\myboxesb{#4}}}%
  \eighttt
  \baselineskip6pt\lineskip0pt\lineskiplimit0pt%
  \hsize25mm%
  \parindent0pt%
  \vfil
  \stringize#4\par
  }%
}

\hbox{%
  \myvboxes{11mm}{1mm}{0mm}{\vskip3mm}%
  \myvboxes{11mm}{1mm}{0mm}{\basevskip3mm}%
  \myvboxes{11mm}{1mm}{0mm}{\vskip1mm}%
  \myvboxes{11mm}{1mm}{0mm}{\basevskip1mm}%
  \myvboxes{11mm}{1mm}{0mm}{\vskip0mm}%
  \myvboxes{11mm}{1mm}{0mm}{\basevskip0mm}%
}

\bye

