The HasAddIn ReferenceTypeis a concrete ReferenceTypeand can be used directly. It is a subtype of the HasComponent ReferenceType.
The semantic of this ReferenceTypeis to bind an AddInto another Nodethat is the source of this Reference. The AddInconcept is described in 4.9.3.
The SourceNodeof this ReferenceTypeshall be an Objector ObjectType. The TargetNodeshall be an Object.
One SourceNodecan refer to multiple AddIns.