This is used by tlgsetup to prepare you input data to support the desired column layout.
column_metadata
A data frame with one row per column for each table type and 6 variables:
identifier used to group a table column layout
distinct variable values used, typically numeric and typically a treatment/main effect variable, think TRT01PN
decode of coldef that will display as a column header in the table
spanning header to display across multiple columns
spanning header to display across multiple columns, second level
spanning header to display across multiple columns, third level