Relationship Handler
A relationship handler is an RDML function or reusable part that is called to dynamically expand the relationship between a parent and child object. By doing this you can improve filter performance by only adding root or parent objects to the instance list initially. For a sample of such handlers see the Sample Relationship Handler Function and the Sample Relationship Reusable Part.
Relationship handlers are used by the shipped instance list only, they are not applicable when writing your own instance list.
This property is in the Business Object Instance List/Relations tab.