A PackedScene typed by its root node type T. Editor-side filtering to scenes whose root is T is provided by the inspector plugin; here the type gives a typed instantiate and a runtime root-type check.
Instantiate the scene and add its root as a child of parent, returning the root as T. T must be a node type (so its root can be parented); a null parent or unassigned scene yields null.
Instantiate the scene and add its root as a child of parent, returning the root as T. T must be a node type (so its root can be parented); a null parent or unassigned scene yields null.