XBL DOM Help Requested

I like the XBL anonymous content model a great deal, but there are a few questions I have unanswered.
I particularly like the proposed <xbl:element/> . If and when it’s implemented, it would give me a lot of flexibility for defining new XBL bindings. You could have a node list represented by an element with the following anonymous content model:

<content>
<children/>
<element/>
</content>

As I’m starting to explore C++ and building Mozilla, I’m thinking maybe this is something I should implement (bug 98712 ). But there are a few points which I don’t think the XBL spec really made clear when it came to how the DOM treats these anonymous nodes and their relationship to bound elements…
XBL Questions
I’d really appreciate any advice on what the blank fields in the document’s final table should be.