Suppose you wanted to add an implementation of invoice for a subclass of Order or Contract.
假設您想爲Order或Contract的子類添加invoice的實現。
"Net Selling Price refers to the gross invoice price of Contract Products sold of otherwise disposed of by Licensee in normal, bona trade, commercial transactions"
We request you to deduct our commission from the invoice.
在這個例子中，路徑invoice/item中的所有元素將被忽略。
And with that, you have polymorphic invoice and manifest functions that can be called on either an Order or a Contract and that will do the right thing.
A record may represent an invoice or a customer, but it never represents an invoice and a customer.
Another example may be where a business policy statement says that additional human task checking is required for invoice transactions are over 10,000 dollars.
此實現是封閉的：在您編譯FulfillmentGenerator類以後，在不編輯原始碼和重新編譯的情況下，您無法將invoice方法擴展到新的類型。
Once the instance is constructed, you can call the invoice and manifest functions on your PurchaseOrder object, which uses the implementations provided in the defrecord.
The orderer must then be prepared to respond to a request (callback, in this case) to process the final invoice.
In this example, all elements in the path invoice/item will be skipped.
Handspring Visor and Visor Deluxe are warranted for one year starting from the day as listed on the customer invoice.
就這樣，您具有多態invoice和manifest函數，可以在一個Order或一個Contract上調用且作出正確*作。
"Net Selling Price"means the remaining sum which the selling commercial invoice price deducts the packing expenses,transportation expenses,insurance premium, commissions,commercial discounts, taxes and expenses for bought out elements and parts etc."
