anchor.diff:  
   @CustomTag('ajax-form')
   class AjaxFormElement extends FormElement with Polymer, Observable {
  -// TODO:
  -// - bind to <input type=submit> elements
  -// -
  +  // TODO:
  +  // - bind to <input type=submit> elements
  +
     static final _VALID_ENCTYPES = <String, _REQUEST_FACTORY>{
         'application/x-www-form-urlencoded': (fields) => new UrlencodedRequest(fields),
         'multipart/form-data': (fields) => new MultipartRequest(fields),
  
positive.code:     }
    }
  
    @ComputedProperty('ajax.progress')
    CoreAjaxProgress progress;
  
    /// Headers to be passed to the ajax request.
    /// headers associated with the content type of the request are added
    /// automatically.
  
negative.code:   static const _ajaxFormError = const EventStreamProvider('ajax-form-error');
    static const _ajaxFormComplete = const EventStreamProvider('ajax-form-complete');
  
    Stream<CustomEvent> get onFormResponse => _ajaxFormResponse.forElement(this);
    Stream<CustomEvent> get onFormError => _ajaxFormError.forElement(this);
    /// An error handler
    Stream<CustomEvent> get onFormComplete => _ajaxFormComplete.forElement(this);
  
    /// The URI of a program that processes the form information.
  