Ref. this Microsoft's official video: http://www.asp.net/web-api/videos/getting-started/custom-validation
I downloaded the code and run it. It's fine.
Then, I remove all the client validation attributes(data-val-*) from the html file. It didn't work fine. I could not see the validation messages on the web page.
My question is how to regular the server side validation messages and how to display them as client-side validation.