[dom] When iterator collection is set?

ArkadiuszMichalski has just created a new issue for 
https://github.com/whatwg/dom:

== When iterator collection is set? ==
"Each NodeIterator object has an associated iterator collection , 
which is a collection rooted at root, whose filter matches any node."
https://dom.spec.whatwg.org/#iterator-collection

But when this collection should be setting, after creating 
NodeIterator, or in some steps in createNodeIterator() method (before 
return this object, but after setting root and filter)?
https://dom.spec.whatwg.org/#dom-document-createnodeiterator


See https://github.com/whatwg/dom/issues/86