By David Mertz, IBM developerWorks

In Part 2 of a serial article on GUIs and XML configuration data, David discusses how XML is used in the configuration of GUI interfaces. He looks at Mozilla's XML-based User Interface Language (XUL) which allows you to write applications that run without any particular dependency on the choice of underlying operating system. This may seem strange at first, but you'll soon see that this Mozilla project offers powerful tools for GUI building that allow you to develop for an extensive base of installed users. Mozilla is now much more than a browser: it is a whole component and GUI architecture. Indeed, Mozilla is more cross-platform and more widely installed on user systems than probably any other GUI library you are likely to consider. What you might think of as general purpose GUI/widget libraries -- Qt, wxWindows, GTK, FOX, MFC, .NET, Carbon, and so on -- have various advantages and disadvantages. But none of them can be assumed to be already installed across user systems. Many of them are only available on a subset of the platforms Mozilla supports, and most are relatively difficult to install or have licensing issues. Mozilla is worth installing just because it is such a great browser; once you have it, you have a free platform for custom applications. To be completely cross-platform in your Mozilla/XUL applications, you need to restrict yourself to configuring GUIs in XUL and programming their logic in JavaScript.

http://www-106.ibm.com/developerworks/library/x-matters35/