title: What's the appropriate HTTP response for invalid data submitted by the user?
body: <p>I'm experimenting with JSON and http response codes. I'm submitting a form via an AJAX request and I obviously need to validate the data on the server-side.</p>
  
  <p>My idea is to respond with a "200 OK" response (with a confirmation message as the body) if the post is successful. I don't know what to respond with if the data that the user sends is invalid.</p>