XML диалект, с който могат да се пишат user interface скриптове, което го прави да е нещо като HTML но изполвайки XML.
… which is a cross-platform language for describing applications’ user interfaces… явно се използва за разработване само на интерфейси.
XUL provides the ability to create most elements found in modern graphical interfaces. Some elements that can be created are:
- Input controls such as textboxes and checkboxes
- Toolbars with buttons or other content
- Menus on a menu bar or pop up menus
- Tabbed dialogs
- Trees for hierarchical or tabular information
- Keyboard shortcuts
In Mozilla, XUL is handled in much the same way as HTML or other types of content are handled. When you type the URL of an HTML page into the browser’s address field, the browser locates the web site and downloads the content. The Mozilla rendering engine takes the content in the form of HTML source and transforms it into a document tree. The tree is then converted into a set of objects that can be displayed on the screen. Style sheets (CSS), images, and other technologies are used to control the presentation. XUL functions in much the same way.
https://developer.mozilla.org/en-US/docs/Archive/Mozilla/XUL/Tutorial