To get the hierarchy of the user interface elements you can insert the command UIATarget.localTarget().logElementTree();
Studying the output of this command you will be able to guess the correct expression. In some cases you need to wait until every item is created (for example with UIATarget.localTarget().delay(1);
) before logging.
An other oportunity to get the right answer is to record with Instuments as you fill this textfield (manualy) and check the generated code.