Hi Alex,
As far as I know, there is no document.
You just assume the paths using Easy Form Editor.
Applications and Unser Management-> Form Template Maintenance :
1. Select the template and Edit with Easy Form Editor
2. On Easy Form Editor window, click Add Row and there, you can find the paths.
User "-" to access the child elements just like you used for Purchase Order.
[PurchaseOrder-SellerParty-ContactPerson-FormattedName]
(FYI : Not all paths work correctly. Need to use Trial and Error approach.)
Best Regards,
Fred