Today I was examining request validation mode in ASP.NET 4.5 and observed some interesting behavior while using it with server control. With ASP.NET 4.5, Request Validation Mode introduced two new features called deferred or lazy request validation and access to unvalidated data.
Before ASP.NET 4.5, request validation was triggered either for each and every request data in beginning phase of request processing or if it is disabled then it triggers for none of them. In ASP.NET 4.5, lazy request validation feature is introduced which ensure that only required request data are validated only when it is accessed by code. To enable lazy request validation set requestValidationMode attribute to 4.5 in httpRuntime element in web.config.