What do you do if XML information is split across several documents? You need some kind of merging or component technology, but XML doesn't have either. The Mozilla platformthe technology behind the Mozilla and Netscape applicationshas a neat solution to this problem. Documents written in Mozilla's XUL dialect of XML can be merged automatically into a single, final document. That's done using a system called overlays, and that overlay system is described in this article. Overlays are suitable for web engineers who are serious about quality of design (and for hackers, too).
XUL (pronounced "zool" if you're cool) is described in the first article in this series, "An Introductory Tour of Mozilla's XUL."