DocumentTraversal

Is there a parser-independent way to obtain a DocumentTraversal interface?
The doc here:

	http://www.w3.org/TR/2000/CR-DOM-Level-2-20000510/traversal.html

shows the following:

	NodeIterator iter = (DocumentTraversal)document).createNodeIterator(
          root, NodeFilter.SHOW_ELEMENT, null);

Does this imply that the class implementing the (DOM Level 2) Document is
guaranteed to also support DocumentTraversal?  How else would one get at it
otherwise?