!3 Column Fixtures have a virtual Execute() method which is called before the first output operation in a given row. You can override this method to handle some processing after input/before output.
----
!|ExecuteExampleFixture|
|int field|int field?|
|1|2|
|2|4|

{{{
	public class ExecuteExampleFixture : ColumnFixture
	{
		public int IntField;

		public override void Execute()
		{
			IntField = IntField*2;
		}
	}
}}}