When node.ownerDocument is not window.document?

Question

I'm looking at MDN and W3C resources to find out what exactly is ownerDocument and how it works?

As I tested in any condition node.ownerDocument == window.document. So when this property is not window.document?

Can you explain it?

Answer 1

One way is if the node was obtained from an iframe or secondary browser window.

Another way is if it's a node from an XML document obtained from an HTTP source via AJAX.