I don't think they're replacing any objects. Every time a Content-Type of image/gif is encountered it appends a new object to #stream with the image data inlin

I don't think they're replacing any objects. Every time a Content-Type of image/gif is encountered it appends a new object to #stream with the image data inlined. I was really confused at the object tags at first, so I went ahead and copy pasted one of the object tags with image data into a blank html and loaded it into firefox. The image showed up fine. This is an extremely clever solution. I know jQuery UI's icons are in one giant image file and background offsets are used to display the correct icon, but this is probably better for a dynamic solution because the amount of CPU it would take to stitch upwards of 100 images together.