example Custom validation in c# metro applivation

Question

hi, how to customize an Attribute for validation.i need 1 very goood example.

i found this http://stackoverflow.com/questions/4318524/understanding-validationcontext-in-dataannotations

but i have doubt that : 

in 

 m_validationAttributes.Add(new CustomValidationAttribute(typeof(DateOfBirthValidator), "ValidateDateOfBirth"));
       

what i can write in ValidateDateOfBirth ? what is the signature for it?