\def\cals@spanq@heights{{0pt}}
\def\cals@lastWidth{0pt}
\brow

\nullcell{lr}
\show\cals@span@ifL
\show\cals@span@ifT
\show\cals@span@ifR
\show\cals@span@ifB
\def\cals@lastWidth{0pt}
\nullcell{tb}
\show\cals@span@ifL
\show\cals@span@ifT
\show\cals@span@ifR
\show\cals@span@ifB