XUL is an [http://en.wikipedia.org/wiki/Xml XML] based language and thus has a similiar set of advantages. One of the biggest being that it that its completly cross-platform. It accomplishis accomplishes this be by defining the locations and type of each widget but not defining what it will look like. Because of this the user-interface will use the systems native componets to build the GUI and thus looks like a normal native application. XUL also allows for the insertion of other XML languages into it such as [http://en.wikipedia.org/wiki/Xhtml XHTML], [http://en.wikipedia.org/wiki/MathML MathML] and [http://en.wikipedia.org/wiki/Svg SVG]. Also because of its structure all the GUI componets and tezt is localized which makes it easy translate into other languages.