Add a new relation of the specified type with the specified target to the current relation set if the relation set does not contain a relation of that type. If it is does contain a relation of that typea the target is added to the relation.
an #AtkRelationType
an #AtkObject
Add a new relation of the specified type with the specified target to the current relation set if the relation set does not contain a relation of that type. If it is does contain a relation of that typea the target is added to the relation.