expression.ControlSource
expression Required. An expression that returns an ElementExtension object.
Remarks
This property returns or sets the values of the Name and Source properties for the field to which the specified control is bound. The property values are returned as a string in the following format: "PageField.Name:PageField.Source" where the strings in italics are replaced with the actual values of the Name and Source properties. If the Name and Source property values are identical, only one value is returned.
If you set this property to the name of a schema field in a schema row source used by the section containing the specified control, the schema field is automatically added as a page field.