This specifies the number of columns to be in the left pane. Note that this counts physical columns that have a non-zero data width, whether or not the column is hidden, and it is based on the order in which they are defined in the coldef parameter (not necessarily the order they appear in the physical input data.) So columns which use cpos and cwidth of 0 do not count, but all other columns do (including the special column needed for multi-level support, hidden color columns, etc.)