Silverlight 4 Validation

This two-part series sums it up:
http://www.silverlightshow.net/items/The-validation-story-in-Silverlight-Part-1.aspx
http://www.silverlightshow.net/items/The-validation-story-in-Silverlight-Part-2.aspx

SL 3 supports ValidatesOnExceptions=True, NotifyOnValidationError=True
Throw exceptions in setters. Optionally use validation attributes on model properties: this requires Validator.ValidateProperty(value, new ValidationContext... in setter
Can use CustomValidation attribute and sdk:ValidationSummary tag

SL4 introduces IDataErrorInfo plus ValidatesOnDataErrors=True tag
and INotifyDataErrorInfo plus ValidatesOnNotifyDataErrors=True

Can customize the validation states in Blend: Default transition, Valid, InvalidUnfocused, InvalidFocused