Wikipedia
XFrames is an XML format for combining and organizing web based documents together on a single webpage through the use of frames. Similarly to HTML Frames, XFrames can be made useful through its power to create a content frame that is scrollable while other frames - such as sidebar menus, the header and footer remain in place on the page. XFrames will be particularly useful to web developers who will be able to modify a single document and have that modification appear on all pages that contain the document within a frame.
The main advantage of this next generation of frames is that it overcomes several of the major usability problems existing in the traditional framing system.
Although still in the working draft stages, XFrames will be replacing traditional HTML Frames.