ReferenceGrabReceiver component as seen in the Scene Inspector
The ReferenceGrabReceiver component can receive a reference dropped onto a UIX element Button by a user. The reference dropped is then stored into the field specified by TargetReference (an example would be to use the ReferenceField).
Letting go when the reference you want to send into the TargetReference field, is currently the way on how it can trigger.
Combining this with the ReferenceProxySource component is a powerful way of moving references around without the need to open a Scene Inspector. Having a ReferenceField of IWorldElement as the TargetReference is the most recommended way of successfully transferring a reference this way.
Examples
This can be used to allow the user to put in slots, music, or even value fields in a UIX canvas/panel for installers/settings for different systems.