(This section is still under construction.)
It is highly desirable that SVG provides a mechanism by which other XML language processors can render into an area within an SVG drawing, with those renderings obeying the various transformations and styling information that is currently active within the SVG document. One particular example of this would be to provide a frame for the HTML/CSS processor so that dynamically reflowing text (subject to SVG transformations and compositing) could be inserted into the middle of an SVG document. Another example is inserting a MathML expression into an SVG drawing.
The exact mechanism for providing this capability hasn't been decided yet.