Validation.ErrorTemplate Attached Property
Gets or sets the ControlTemplate used to generate validation error feedback on the adorner layer.
Assembly: PresentationFramework (in PresentationFramework.dll)
The WPF data binding model allows you to associate ValidationRules with your Binding object. If the user enters an invalid value, you may want to provide some feedback about the error on the application user interface (UI). One way to provide such feedback is to set the Validation. to a custom ControlTemplate.GTMT
For a detailed discussion of validation, see the Data Validation section of the Data Binding Overview.