title: on what http status codes are ajax failure/error callbacks called?
body: <p>for a standard ajax call :</p>
  
  <pre><code>$.ajax({
        url: 'http://www.nodomainajaxcallhere.fail/busted.nogo',
        error: ----,
        failure: ----,
  ...
  })
  </code></pre>
  
  <p>I thought that any respond with status code 200 is success and all other are automatically failure. But today I first saw "error" callback.</p>
  
  <blockquote>
    <p>when is the failure callback called?  on a connection error? 
    when is the error callback called? on any other exception? http status code
    400 ?</p>
  </blockquote>