XUL

Description

XUL which is pronounced zool stands for XML User Interface Language is a Mark-up language used primarily in Mozilla applications. XUL is used to define what the user interface will look like such as buttons and other widgets but it is not used to define how those item will look.

Discussion

XUL is an XML based language and thus has a similiar set of advantages. One of the biggest being that it that its completly cross-platform. It accomplishes this 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 native application. XUL also allows for the insertion of other XML languages into it such as XHTML, MathML and SVG. Also because of its structure all the GUI componets and tezt is localized which makes it easy translate into other languages.

Currently, an application named XULRunner is being developed to offer a runtime environment for XUL applications.

Common Usages

• Chrome
• Firefox Extension's GUI

Supported Technologies

• HTML 4.0 and XHTML
• CSS2 and some of CSS3
• DOM2 and some of DOM3
• XML
• MathML
• RDF
• XSLT
• XPath
• Simple XLinks
• XPointer
• XML Base
• FIXPtr
• XML-RPC
• SOAP (Simple Object Access Protocol)
• WSDL (Web Services Description Language)
• ECMAScript/Javascript
• XBL (eXtensible Bindings Language)
• GIF, JPG, PNG, BMP, ICO images
• HTTP 1.1

Technical Details (Technologies XUL relies on)

eXtensible Bindings Language (XBL)

• Allows for additional, custom tags
• Can provide new event handlers and methods for existing elements

Overlays

• Used to customize applications
• Gets around NPL & MPL licensing

XPCOM

• A means of calling upon the underyling C/C++ libraries for heavylifting

XPInstall

• Provides an install tool for distributing XUL applications

Sample Code

<?xml version="1.0"?>
<?xml-stylesheet href="chrome://global/skin" type="text/css" ?>
<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
        align="center" pack="center">
  <description>Is XUL cool or what?</description>
  <radiogroup>
    <radio id="yes" selected="true" label="Yes!"/>
    <radio id="no" label="No wai"/>
  </radiogroup>
  <button id="dpsbutton" label="DPS909 is fun" />
</window>

Paste the above sample code inside your favourite editor and save it with a file extension of .XUL. Open the file in a Mozilla-based browser to view it.

• Line 1: Declares that it is an XML file
• Line 2: Used to reference the stylesheets. In this case, the global/skin chrome directories' default global.css file is used. global.css is used to declare all of the XUL elements.
• Line 3: Describes a new window to be drawn, using the namespace http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul. All children of this window are XUL.
• Line 5: Description tag is like a label, but can wrap many lines.
• Lines 6-9: Describes a radio button group.
• Line 10: Draws a button.

Example Applications

• Mozilla Amazon Browser (MAB) - Rich web application that allows for searching of Amazon's content across their 6 websites (US, Canada, UK, Japan, Germany and France). Can be used through the web or downloaded to the desktop.
• XUL Periodic Table - Demonstrates many of the visual capabilities of XUL.

Newsgroups, Mailinglists, IRC Channels

• mozilla.dev.tech.xul newsgroup (alternatively, use Google Groups)
• dev-tech-xul mailinglist (manually use dev-tech-xul@lists.mozilla.org)
• #xul on irc.mozilla.org

Resources

• XUL Programmers Reference
• XUL 1.0 Specification
• XUL tutorial
• XUL new features and enhancements