[Maya] API concept of the World as a parent?

Coding
1

If I want to track when nodes are reordered, I need to attach a callback to the parent, but what if the nodes I want to track are all parented to the World?

http://help.autodesk.com/view/MAYAUL/2015/ENU/?guid=__cpp_ref_class_m_dag_message_html

How do I go about getting the World as an MDagPath? In the documentation for MDagPath it says:

“A DAG path is a path from the world node to a particular object in the DAG.”

http://help.autodesk.com/view/MAYAUL/2015/ENU/?guid=__cpp_ref_class_m_dag_path_html

but what if the parent is the world itself?

Thanks.