Events
One of the key issues the CDF group has been tackling over the past year has to do with events. When you have DOM events (such as a "click" event or a change of "focus") in one part of the document (say, the XHTML part) these events may need to propagate to one or more child (SVG) documents and vice versa. This kind of event propagation can enable interactivity features (such as an SVG animation kicking off in one part of the screen when the user selects an item in another part of the screen).