Getting subdocuments (iframes) using ISimpleDOMNode

What is the best way to retrieve a subdocument through traversing using ISimpleDOM* interfaces?

Currently, I'm QIing to IAccessible when the node name is an iframe but it only works some of the time (as documented). When I have IAccessible I get the number of children and if there are any I QI to ISimpleDOMDocument and then can get the root of that subdocument from there and traverse using ISimpleDOMNode again.

There is also no NODETYPE_DOCUMENT* types either beyond the root document that I've seen. I'm not sure if this is a bug, not really supported, or if I'm doing it wrong but this is not documented anywhere I've seen.

Thanks in advance.