Defined expressions for extracting the appointment number in Label Designer

Summary:

I want to print the field appt_nbr on a ibcontainer label, but I have not been able to find the correct expression. I have already tried the following:

u"~appointment.appt_nbr""~appointment.appt_nbr"
dict_get(get_obj(), "appointment.appt_nbr")
~shipment.appt_nbr
~shipment.appointment.appt_nbr
~container.appointent.appt_nbr

Neither of these works - they just return None on the label.

Could you please tell me where I can find a list of all available fields in Label Designer?

Content (please ensure you mask any confidential information):

ibcontainer label

Version (include the version you are using, if applicable):