ID of the DataCollection.

If the DataCollection is a KeyedCollection, each inner DataField corresponds to an option element. The combo box uses the field ID as the option label and the field value as the option value.

If the DataCollection is an IndexedCollection, the inner elements must be KeyedCollections, and the item and value attributes are mandatory. Each inner KeyedCollection corresponds to an option element. The list uses the collection field named in the item attribute as the label and uses the collection field named in the value attribute as the option value. If the data element named dataName contains the value of an option element, the combo box highlights this option element as selected (it is the default).