How to use the "SO_PickingSheetPrinting" method "SelectOrder" to queue sales order picking sheets to be printed

From a BOI script I would like to select individual orders so that a type "4" record will be added to "SO_SalesOrderPrint" table. The method "SelectOrder" calls for two separated string parameters: "hdrRec$" and "dtrRec$". This is confusing. Why would the Object Reference documentation say that the "hdrRec$...is currently not being used by this routine". I would expect that's the only way to pass the order numbers. I might expect the "dtlRec$" parameter to say that b/c I don't know why the "SO_PickingSheetPrinting" would need to know about the detail records.