DomainUpDown control is one of the new controls available in the Silverlight 3 Toolkit which can be found in
Silverlight Toolkit
This control Represents a Windows spin box (also known as an up-down control) that displays string values.Help files for the assemblies are downloaded with them by default. This control belongs to the following namepsace.
Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
The control is bound with a datasource collection.