Every column definition has a column type (that specifies what values are allowed in the column) as well as flags that specify whether the column is hidden, required, etc. This is adequate for many apps, but sometimes a more dynamic or data-driven mechanism is needed. This is what Column Constraints provide -- a column constraint is an expression that is dynamically computed to determine the behavior of a specific column. Three different column constraints can be defined for each column: Show_If Valid_If Required_If To add a column constraint, use the Column Structure tab of the Data pane in the Advanced Editor and click the "Edit" icon at the left of the corresponding column definition.