code: function(arg, typeSpec) {
  				var result = new Deferred();
  				var predictions = this._getPredictions(arg.text, typeSpec);
  				result.resolve(this._createCompletion(arg.text, predictions));
  				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.