code: function(arg, typeSpec) {
  				var result = new Deferred();
  				this._getPredictions(arg.text).then(
  					function(predictions) {
  						result.resolve(this._createCompletion(arg.text, predictions, typeSpec));
  					}.bind(this),
  					function(error) {
  						result.error(error);
  					}
  				);
  				return result;
  			}
docs: This function is invoked by the shell to query for the completion
  status and predictions for an argument with this parameter type.