+=item po_number
+
+Purchase order number (normally not required).
+
+=item tax
+
+Tax amount (portion of amount field, not added to it).
+
+=item freight
+
+Freight amount (portion of amount field, not added to it).
+
+=item duty
+
+Duty amount (portion of amount field, not added to it).
+
+=item tax_exempt
+
+Tax exempt flag (i.e. TRUE, FALSE, T, F, YES, NO, Y, N, 1, 0).
+