How do I record an element that consists of multiple parts?

HUMBLE uses the NL-SfB coding, which is prescribed in the NEN 2767. By creating an element, related components can then be added to the primary element. For instance, an air handling unit. It includes the cabinet itself, but also the ventilation fans and the control valves.

In this case the main element is the air handling unit, underneath it are the related elements (fans and control valves).