When a lookup screen is invoked by openLookup() method, it displays a panel at the bottom with the buttons designed to pass an instance of the currently selected entity to the calling code. That is the main difference between lookup and simple screen. When being invoked by openWindow() method or, for example, from the main menu, the panel with the buttons is not displayed.

Lookup screens are recommended to be used to display lists of entities. Visual components intended to display and edit links between entities (such as PickerField, LookupPickerField, SearchPickerField) invoke lookup screens to find related entities.

For standard actions to work correctly, an identifier of a lookup screen in screens.xml should have the format of {entity_name}.lookup, for example, sales$Customer.lookup.

The controller of a lookup screen should be inherited from the AbstractLookup class. The lookupComponent attribute of the screen’s XML should refer to the component (for example Table), from which the selected entity instance should be taken as a result of the lookup.