The general concept is that annotations will be used to decorate the model with constraint definitions. For example:
public class MyModel
{
[Required]
[ConstrainLength( minLength=1, maxLength=100 )]
public var aString: String;
[ConstrainRange( minValue=-123.4, maxValue=234.5 )]
public var aNumber: Number;
}
The intention from here is that there will be functionality for automated validator generation and API-based constraint checking.
Stay tuned for more.