The DefinitionKey attribute can be assigned to properties of your selected object to define which EditorDefinition to be applied to the property. As an alternative to the Editor attribute, this allows you separate the UI-specific code from your business model code. It can also be used to specify a specific default editor when a property type does not resolve to a valid editor (e.g., Object). This feature is only available in the "Plus" version. Click here for more details about Xceed Toolkit Plus for WPF.