code: function() {
  
      var types = [].slice.call(arguments);
  
      this._respondsTo || (this._respondsTo = []);
  
      if (types.length) {
        this._respondsTo = this._respondsTo.concat(types);
      }
  
      return this._respondsTo;
    }
docs: register the format / types this controller responds to when response
  is delegated to the autoresponder
  
  @return {String} mime short-type ex. 'json', 'html'