columnOrder

Column keys in the order the user put them, or empty while they are in declared order.

Columns the list does not name follow the ones it does, in declaration order — which is where a column added since a layout was saved appears. Assigning an empty list puts every column back where its header declares it.

With grouped headers the order applies to every level of the tree at once, and a group moves as a block — a column cannot be taken out of the group it was declared in.