You have probably noticed
that most PROC TABULATE tables have a big empty box in the table grid.
The box sits above the row headers and to the left of the column headers.
It would be nice if we did not have to waste this space. As it happens,
you can take advantage of that space. You can use that space to hold
some descriptive text or the value of some variable. But the real
advantage of this space is that for three-dimensional tables, you
can use it to hold the value of the page variable(s).