DoCellUpdate
DoCellUpdate = function(rowFrame, cellFrame, data, cols, row, realrow, column, fShow, table, ...)
fShow == true, update your display, the cell is showing.
fShow == false, your cell is being hidden (most likely because your table is large and you only have a few rows of data to actually display) so clear it out.
For other users of this routine: you do not need to handle any ellipsis arguments unless you're passing them through to a default update function. Nothing is passed to any cell updater after the lib-st table reference in 'table' (bad name, sigh).