This optional property allows you to explicitly specify a separate ControlSource expression for unbinding back into the underlying data source. Use this if you need to bind to methods rather than properties or to read and write into separate underlying properties.

The value is assumed to be a property name by default.

To use an expression prefix the expression with an =. To get the captured input value already converted to its proper type use {0} as a placeholder in the expression:

UnBind to a simple property:
ControlSourceUnbindExpression="MyPropertyName"

UnBind an expression to a method:
ControlSourceUnbindExpression="=this.Page.oBusiness.SetValue('MyProperty',{0})"