Any nested object. For example, a Customer object:
Customer
-Name
--FirstName
--MiddleInitial
--LastName
-Address
--AddressLine1
--City
--State
--Zip
-Contacts[] // This is a collection of Contact objects
--Name
---FirstName
...
--EmailAddress[] // This is a collection of strings representing the email addresses
--Phones[] // This is a collection of phone objects
---AreaCode
---Number
---Extension
---PhoneType