ScriptObject.SetProperty Method (String, Object)
Sets a property that is identified by name on the current scriptable object.
Assembly: System.Windows.Browser (in System.Windows.Browser.dll)
It is possible to set a property value for a non-existing property. In this case, the browser adds the property as an expando on the object.
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.