Using LAST in a map rule to reference an output

In a map rule, when referencing an output, LAST refers to the last built occurrence of that object. For example, using the same expression:

PO# Field:Order = PO# Field:Order[LAST]

LAST refers to the previous occurrence of Order because, when this rule is evaluated, the last known Order is the last one built.

LAST is a reserved word and is not case sensitive.