title: Passing the error message to jQuery File Upload
body: <p>I've integrated <a href="https://github.com/blueimp/jQuery-File-Upload/wiki">JQuery File Upload</a> into a Java Spring application. The returned JSON is generated from an array of Picture, where Picture contains "name", "size", "url", "thumbnail_url", "delete_url" and "delete_type". </p>
  
  <p>Sometimes I decide to not accept the upload on the server, to reject it, because of missing pre-conditions, so I would like to inform inform the user about it, by returning to the client an error message.</p>
  
  <p>I know it's possible to return an error message and an error code to the File Upload plugin, but I can't find it in the documentation. I suppose that I've to add two fields similar to "error_message" and "error_code". </p>
  
  <p>Where can I find this documentation or what are the field names that I should return.</p>