Each derived property must have one or more expressions defining the criteria for searching the result elements.
Warning
It is strongly recommended that you specify the customization target in the customization element before defining the expression for its derived property.
To open the dialog for a new expression definition
In the general specification pane (opened by default), click the Expression property and then click the ... button. The Expression dialog opens, and you can then construct predefined expressions or define your custom operation for calculating derived property values.
