In general, that's going to be very dangerous as to do it would effectively allow arbitrary HTML, which is a big security issue. (SVG can also embed JavaScript, which is another issue.) In general, I don't think the inline XML approach is necessarily ideal; doing it would likely also require custom PHP for rendering as we would normally escape it. I'm not sure what your needs are, but image embedding should work out of the box (though we don't support it in the image proxy, due to the JS embed issue).