A way to think of what is occurring is as a union of sorts between the existing interface and the file being imported so that the two become one. Practically it means that we don't have to navigate the documents via a frame based or window instance based approach.
At this point you should be starting to note that a genesis for an image gallery is starting to form. We can use the earlier technique of importing xml files to provide information about the image and we now just have learned how to import the image itself. So the basic functionality for an image gallery widget is in place, but will obviously need refinement to work effectively.
Before we move onto that though, I want to demonstrate a few other things about importing different media with xmlhttprequest.