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XUL

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XUL
ParadigmDeclarative (markup language)
DeveloperMozilla Foundation
Implementation languageC++
PlatformGecko
OSCross-platform
LicenseMPL
Filename extensions.xul
MIME type: application/vnd.mozilla.xul+xml
Websitehttps://developer.mozilla.org/en-US/XUL
Major implementations
Mozilla
Influenced by
HTML, XML

XUL (/ˈzuːl/ ZOOL), which stands for XML User Interface Language, is a user interface markup language developed by Mozilla. XUL is implemented as an XML dialect, enabling graphical user interfaces to be written in a similar manner to web pages. Such applications must be created using the Mozilla codebase (or a fork of it); the most prominent example is the Firefox web browser.

In the past, Firefox permitted add-ons to extensively alter its user interface via custom XUL code, but this capability was removed in Firefox 57 and replaced with the less-permissive WebExtensions API.[1][2] (Three forks of Firefox still support the legacy capability: Pale Moon,[3] Basilisk,[4] Waterfox.[5])

History

XUL was devised at Netscape in 1997 as part of the development effort that eventually became the Mozilla codebase.[6] It never gained much traction outside of Mozilla or its forks. In the early 2000s there was some interest in using XUL by other parties, including Amazon,[7] but that dried up with the advent of HTML5.

With the release of Firefox 57 in 2017, Mozilla removed support for legacy add-ons, including the use of custom XUL code.[1][2] This was a key step in the organization's long-term goal of reducing XUL usage in Firefox and replacing it with HTML5 alternatives.[8]

Usage

XUL can only be used with the Mozilla codebase (or a fork of it) because the Gecko and Goanna enginesare the only ones capable of parsing and rendering XUL.[9]

Application programmers need to define a XUL interface as three discrete sets of components:

  1. Content: the XUL document(s), whose elements define the layout of the user interface
  2. Skin: the CSS and image files, which define the appearance of an application
  3. Locale: the files containing user-visible strings for easy software localization

XUL defines a wide range of elements, which roughly belong to the following types:

XUL documents can contain elements from other XML dialects, such as SVG or MathML.

Example

This example shows three buttons stacked on top of each other in a vertical box container:[10] 

<?xml version="1.0"?>
<?xml-stylesheet href="chrome://global/skin/" type="text/css"?>

<window id="vbox example" title="Example 3...."
xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
  <vbox>
    <button id="yes1" label="Yes"/>
    <button id="no1" label="No"/>
    <button id="maybe1" label="Maybe"/>
  </vbox>
</window>

XUL platform: UXP

While Mozilla abandoned XUL and Gecko as an open platform to build XUL applications on, with on-going work to remove XUL and XPCOM extension support from its source tree and the Firefox browser[11][12], independent development was started on continuing use of the XUL language as a multi-application platform with XUL-based extensibility. This effort is the Unified XUL Platform or UXP[13], and is the current application platform used for Pale Moon, Basilisk, the Hyperbola project's continuations of Iceweasel (Iceweasel-UXP)[14] and Icedove (Icedove-UXP)[15], the Interlink mail and news client[16], and the Ambassador IRC client[17].

UXP builds on the Gecko fork Goanna to provide independent development of the layout and rendering engine used by application building on the platform, unrelated to Mozilla's direction. The platform offers support for NPAPI Plug-ins and XUL-based extensions as well as full theming of applications building on it, and offers a choice from a broad set of features for use in applications that may not necessarily be required for current individual applications, to provide maximum flexibility. Most of these features (like EME and WebRTC are selected at build time to keep resulting applications focused on their specific tasks.

Ghostbusters reference

The villain of the 1984 film Ghostbusters was a deity called Zuul who possesses the character Dana Barrett and declares, "There is no Dana. There is only Zuul".[18] The creators of XUL, which is pronounced the same as Zuul, made the slogan "There is no data. There is only XUL!", part of which became the XML namespace.[19]

See also

References

  1. ^ a b Firefox 57 release notes
  2. ^ a b Kev Needham (2015-08-21). "The Future of Developing Firefox Add-ons". blog.mozilla.org. Retrieved 2018-04-02.
  3. ^ "Pale Moon future roadmap". Pale Moon. Retrieved 2018-04-02.
  4. ^ "Pale Moon team releases first version of Basilisk browser". ghacks.net. 2017-11-17. Retrieved 2018-04-02.
  5. ^ "Waterfox, Its Legacy and Looking to the Future". Waterfox blog. 2018-04-28. Retrieved 2018-06-20.
  6. ^ Jorge O. Castro (2004-06-15). "Ars Technica sits down with Scott Collins from Mozilla.org". Ars Technica. Retrieved 2018-11-28.
  7. ^ "Remote Application Development with Mozilla, Part 2: A Case Study of the Mozilla Amazon Browser (MAB)". Oreillynet. 2003-02-05.
  8. ^ "Life After XUL". Mozilla. Retrieved 28 November 2018.
  9. ^ "Gecko FAQ". Mozilla Developer Center. Mozilla Foundation. 2008-03-15. Retrieved 2009-03-26.
  10. ^ The Box Model - XUL | MDN. Developer.mozilla.org (2012-12-16). Retrieved on 2014-03-28.
  11. ^ post 57 api changes (bugzilla)
  12. ^ The War on XBL (bugzilla)
  13. ^ UXP on GitHub
  14. ^ Iceweasel-UXP project page
  15. ^ Icedove-UXP project page
  16. ^ Interlink Mail & News
  17. ^ Ambassador (IRC client)
  18. ^ Ghostbusters clip
  19. ^ Mozilla XML Namespace
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