=over 4
-=item receipt_number() / sales_number()
+=item receipt_number()
-Receipt number and sales order number of submitted order.
+Receipt number of this transaction; this is actually a string, unique to all
+InternetSecure transactions.
+
+=item sales_number()
+
+Sales order number of this transaction. This is a number, unique to each
+merchant, which is incremented by 1 each time.
=item total_amount()