I just googled for about 2 hours and didn\'t find anything.
Given the following scenario:
public class Person
{
[Required]
public string Name
It seems, based on the support provided in the framework, that your extraordinary idea to "Validate" a text field is so rare and uncommon that it needs not to be considered at all. We all know that if what you wanted to do was at all common or useful, there would be some consideration for such a feature in such a well designed and comprehensive framework.