In section 3.15, it says:
If a Print Provider receives a StockLevelRequest, it SHALL send to the Print Buyer a StockLevelResponse whose @BusinessRefID references the StockLevelRequest.
However, in section 6.5.7, it says:
The Print Provider SHOULD respond with a list of items in a StockLevelResponse that references the StockLevelRequest.
So, which is it: SHALL or SHOULD?
My vote is for SHALL.
6.5.7 Catalog and warehouse exchange
A Print Buyer MAY request a report on available items by sending a StockLevelRequest to the Print Provider. Available items
can include both preprinted items that are on stock and custom product types that will be printed individually.
The Print Provider SHOULD SHALL respond with a list of items in a StockLevelResponse that references the StockLevelRequest.