If a GraphObject (or a reference to one) is provided to the RGGProducer (the right side of a rule) it automatically creates a GraphInstance. This works similar to a instantiation rule and creates a single object in the project graph that visualizes to the content of the graph objects. This can also be used inside the instantiation rule of an module.

protected void init ()
[
    Axiom ==>graphobject("objects.obj");
]

This can be seen in the examples:graphexplorer/GraphObjectRef