Normally, validation is handled on the server-side by using a built-in control or writing a method to check the values on the form. On the client-side, JavaScript would be eliminated to the browser. So the jQuery validation plugin was updated to support unobtrusive validation.
Unobtrusive validation helps to reduce the capturing on the user’s interaction with the web application.
Instead of generating JavaScript inline, HTML5 data-* attributes are added to the appropriate form elements.
In ASP.NET 4.5, the jQuery validation plugin is used and the unobtrusive validation functionality is allowed by default.