Cell-Columns-Span
This property allows you to group several cells on the x-axes in the column heading.
The value of this property specifies how many cells should be merged together on the x-axes starting from the column identified by the X property in the row identified by the Y property. The row must be part of the column heading.
Point the first of the merged columns to inquire or modify the content of the merged cells.
 
Example - In a grid where the first three rows are column headings, merge column number 2 and 3 within the second row and put the title "Col.2" into the merged cells
procedure division.
...
  modify screen-1-gr-1(2, 2cell-columns-span 2
  modify screen-1-gr-1(2, 2cell-data "Col.2"
...