\def\cals@lastWidth{2pt}
\def\cals@rs@spec@ll{2pt}
\def\cals@rs@spec@bl{2pt}
\def\cals@rs@spec@bt{2pt}
\def\cals@current@rs@above{}
\def\cals@current@rs@below{}
%
\colwidths{{100pt}{200pt}{300pt}}
%
\cals@span@height=20pt \relax
\show\cals@spanq@heights
\brow\def\cals@lastWidth{0pt}
\nullcell{tr}
\show\cals@spanq@heights
\brow\def\cals@lastWidth{0pt}
\nullcell{br}
\show\cals@spanq@heights
%
\cals@span@height=40pt \relax
\showthe\cals@span@height
\let\cals@borderL=\relax \brow\def\cals@lastWidth{0pt}
\nullcell{lt}
\showthe\cals@span@height
\show\cals@spanq@heights
\brow\def\cals@lastWidth{0pt}
\nullcell{bl}
\showthe\cals@span@height
\show\cals@spanq@heights