Column groups are named groups of contiguous columns.

Column groups have the following behavior:

• Rendering
  • A column group is indicated by a column group header cell that is rendered above and spans across all of its member column header cells.
  • Cells that are in the column grouping row but aren't in a grouped column should have their row span set to 2.
  • The column group header cell's text value should be the 'display name' of the column group. This display name can be different from the programmatic name of the column group.
• Selection
  • If a column group is selected, all of its member columns are selected.
  • A column group is automatically considered selected if all columns in the group are selected. The column group header cell should be rendered as selected.
• Resize
  • Columns within a column group can be resized. The width of the column group header is always equal to the total width of all of its member columns.
• Expand/Collapse
  • Collapsing a column group hides all columns within the group except the leftmost viewable column
  • Expanding a column group shows all viewable columns within the group
  • The column group header should have a decoration indicating whether the column group is expanded or collapsed.
• Reorder
  • Reordering a column not in a column group within the bounds of a column group adds the column to the column group
  • Reordering a column in a column group outside the bounds of the column group removes the column from the column group
  • Reordering a column in a column group outside the bounds of the column group and into the bounds of another column group removes the column from its original column group and adds it to the destination column group
  • Reordering a column within a column group simply reorders the column group. The column remains part of the column group
  • Reordering an entire column group reorders all of the columns within the column group to the destination location