Rename ArtDeliveryRequest to ContentDelivery
Rename ArtDeliveryResponse to ContentDeliveryResponse
Since Content can also refer to CSV etc this name makes more sense.
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A Print Buyer or a Print Provider sends SHALL send a Cancellation to cancel a previously sent PurchaseOrder.
Note: A Print Buyer will typically cancel a PurchaseOrder if the Print Product is no longer required, whereas a Print Provider
will typically cancel a PurchaseOrder if no useable artwork content has been provided within a deadline.