Field help (FORSEL) 

You can only use this field if the Component (field CPNITMREF) field is blank. Instead of entering all the possible options/variants as individual components you can use a predefined 'Component selection' formula to select components. The components selected by the formula are offered when this BOM is added to a sales transaction. A filter on the Deliverable or Cannot be delivered status of the component is applied automatically to ensure the selected components match the status of the parent product.

SEEINFO You can only use one selection formula per sequence number.