XUL

File:PeriodicTableofXUL Windows10 PaleMoon31.png

XUL was devised at Netscape in 1997 as part of the development effort that eventually became the Mozilla codebase.

{{cite web |url = https://arstechnica.com/information-technology/2004/06/collins-interview/2/ |title = Ars Technica sits down with Scott Collins from Mozilla.org |author = Jorge O. Castro |publisher = Ars Technica |date = 2004-06-15 |access-date=2018-11-28}}

XUL is similar to web technologies implemented by the Gecko rendering engine. When XUL was introduced, it added features beyond the then standard HTML 4. It was designed as an extension of HTML to be used with applications rather than documents.{{cite web | url=https://yoric.github.io/post/why-did-mozilla-remove-xul-addons/ | title=Why Did Mozilla Remove XUL Add-ons? |last=Teller |first=David |date=Aug 20, 2020}}

XUL was used by various Mozilla projects, forks of Mozilla projects, and projects closely related to Mozilla. Some software projects such as Songbird, Komodo IDE, and Zotero started as desktop applications that utilized XULRunner to render and compose their UI. In the early 2000s, there was some interest in using XUL by other parties, including Amazon,{{cite web|url=http://www.oreillynet.com/pub/a/mozilla/2003/05/02/casestudy2.html |archive-url=https://web.archive.org/web/20120218221243/http://www.oreillynet.com/pub/a/mozilla/2003/05/02/casestudy2.html |archive-date=18 February 2012 |last=King |first=Brian |title=Remote Application Development with Mozilla, Part 2: A Case Study of the Mozilla Amazon Browser (MAB)|work=Oreillynet |date=2003-02-05 |quote=The Mozilla Amazon Browser is an interesting case study for a number of reasons. First, it's a working prototype application, not an example constructed solely for the purpose of demonstrating the technology. Second, it exercises many areas of Mozilla's support for remote development and thus shows off the capabilities, potential, and limitations of remote XUL applications. Finally, it demonstrates Mozilla's support for web services, an important emerging technology for web application development. }}

but those have switched over to HTML5. Many of the features of modern web technologies such as HTML5, CSS3, ECMAScript 5+, WebGL, and WebAssembly that made rich and modern web applications possible, without the need of utilizing legacy NPAPI/PPAPI/ActiveX browser plug-in technologies like Adobe Flash, Silverlight, Java, or Shockwave, also made much of XUL redundant.

Mozilla released Firefox 57, also known as Firefox Quantum, in November 2017. As part of this, Firefox finished transitioning to a multiprocess architecture. Although XUL add-ons could work in this architecture, they often created significant performance issues. Because of this, Mozilla removed support for legacy add-ons, including the use of custom XUL code. Mozilla switched their browser extensions system to the cross-browser WebExtensions API, which is largely based on the Chrome extension API. In late 2017, Firefox still included 289 XUL bindings for native browser components. By the end of 2019, Mozilla had removed all XUL files from their mozilla-central repository.{{cite web | url=https://wiki.mozilla.org/Firefox/XUL_and_XBL_Replacement | title=Firefox/XUL and XBL Replacement |access-date=27 September 2022 |last=Grinstead |first=Brian |date=16 December 2019}}{{cite web|last=Hirsch|first=Jared|date=2 September 2018|title=Life After XUL|url=https://developer.mozilla.org/en-US/docs/Mozilla/Tech/Life_After_XUL:_Building_Firefox_Interfaces_with_HTML|url-status=dead|archive-url=https://web.archive.org/web/20181129013045/https://developer.mozilla.org/en-US/docs/Mozilla/Tech/Life_After_XUL%3A_Building_Firefox_Interfaces_with_HTML|archive-date=29 November 2018|access-date=28 November 2018|website=Mozilla Developer Network (MDN) |publisher=Mozilla}}

When Mozilla removed support from Firefox, there were still several applications using XUL. Mozilla began gradually removing XUL support from their email client, Thunderbird. They released Thunderbird 78 without support for XUL-based extensions in 2020.{{cite web|url=https://developer.thunderbird.net/add-ons/updating/tb78/changes |title=Adapt to Changes in Thunderbird 69-78 |website=developer.thunderbird.net |access-date=27 September 2022 |date=2022}}

The SeaMonkey internet suite chose to re-implement XUL for the Firefox Quantum codebase, and the suite's development has subsequently slowed. The Pale Moon developers forked Mozilla's entire Firefox 52 ESR codebase to create the Unified XUL Platform (UXP) for their Goanna rendering engine. UXP maintains the traditional XUL capabilities.{{cite web|url=https://forum.palemoon.org/viewtopic.php?f=62&t=17213|title=UXP vs goanna |last=Straver |first=Markus |access-date=27 September 2022 |date=2 November 2017 |quote=The plan is to switch Pale Moon over from our current platform to UXP (long-term plans) because a developed and maintained XUL-based platform is the only way a XUL application (like Pale Moon) has any chance of surviving without falling into obsolescence, with Mozilla abandoning this technology. That has been the main reason why I decided to start on this platform to begin with! Regardless, the platform will not be solely developed for Pale Moon's potential future use, it is developed for any future XUL application that will otherwise be dead in the water. Basically we're taking over the torch from Mozilla in developing and maintaining a platform for XUL applications of any kind; Mozilla should not be seen as "upstream" because it isn't.}} As a result, Pale Moon and other UXP applications have remained single-process but more extensible compared to modern versions of Firefox and Thunderbird.{{cite web |title=There is only XUL |url=http://thereisonlyxul.org/ |archive-url=https://web.archive.org/web/20180917071644/http://thereisonlyxul.org/ |archive-date=17 September 2018 |last=Tobin |first=Matt |access-date=18 September 2018}}

XUL can only be used with the Mozilla codebase (or a fork of it) because the Gecko (or Goanna) engine does the XUL rendering.{{Cite web|title=Gecko FAQ {{!}} MDN|url=https://developer.mozilla.org/en-US/docs/Gecko/FAQ|access-date=2021-01-05|website=developer.mozilla.org|archive-date=2019-10-08|archive-url=https://web.archive.org/web/20191008071852/https://developer.mozilla.org/en-US/docs/Gecko/FAQ|url-status=dead}}

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:

• Top-level elements: window, page, dialog, wizard, etc.
• Widgets: label, button, text box, list box, combo box, radio button, check box, tree, menu, toolbar, group box, tab box, color-picker, spacer, splitter, etc.
• Box model: box, grid, stack, deck, etc.
• Events and scripts: script, command, key, broadcaster, observer, etc.
• Data source: template, rule, etc.
• Others: overlay, iframe, browser, editor, etc.

The default behavior of XUL widgets can be altered with XBL bindings.

{{main|XBL}}

XML Binding Language (XBL) is an XML-based markup language for altering the behavior of a XUL widget, such as a scroll bar.{{cite web|author=Castro|first=Jorge O.|date=2004-06-15|title=Ars Technica sits down with Scott Collins from Mozilla.org|url=https://arstechnica.com/information-technology/2004/06/collins-interview/2/|url-status=live|archive-url=https://web.archive.org/web/20180222104837/https://arstechnica.com/information-technology/2004/06/collins-interview/2/|archive-date=2018-02-22|access-date=2018-11-28|website=Ars Technica|page=2}}{{cite web|title=XBL 2.0 Acknowledgments|url=http://www.w3.org/TR/xbl/#acknowledgments|website=www.w3.org}} An XBL file contains bindings, each of which describes the behavior of a XUL widget. The root element of an XBL file is the element, which contains one or more elements. Each element declares one binding, which can be attached to any XUL element. It may also possess an id attribute. A binding is assigned to an element by setting the CSS property -moz-binding to the URL of the binding's file.{{cite web|title=XBL 2.0|url=http://www.w3.org/TR/xbl/|website=www.w3.org}} For example:

scrollbar {

-moz-binding: url('somefile.xml#binding1');

}

This example shows three buttons stacked on top of each other in a vertical box container:{{Cite web|date=2017-12-09|title=The Box Model - Mozilla {{!}} MDN|url=https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XUL/Tutorial/The_Box_Model|access-date=2021-01-05|archive-url=https://web.archive.org/web/20171209141220/https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XUL/Tutorial/The_Box_Model|archive-date=2017-12-09}}

right

xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">

XUL contains a reference to the 1984 film Ghostbusters. The film's antagonist is the fictional deity Zuul, the Gatekeeper.{{cite book |last1=Garcia-Ventura |first1=Agnes |last2=Verderame |first2=Lorenzo |title=Receptions of the Ancient Near East in Popular Culture and Beyond |date=1 March 2020 |publisher=Lockwood Press |isbn=978-1-948488-25-9 |pages=109 |url=https://books.google.com/books?id=-E7VDwAAQBAJ&dq=%22XUL%22+%22zuul%22&pg=PA109 |language=en}} Zuul possesses the character Dana Barrett and declares: "There is no Dana. There is only Zuul."{{cite web |last1=Quinlan |first1=Erin |title='Ghostbusters' turns 30: Revisit film's supernatural wisdom |url=https://www.today.com/popculture/ghostbusters-turns-30-revisit-films-supernatural-wisdom-2d79768136 |website=Today |access-date=25 May 2024 |language=en |date=6 June 2014}} The creators of XUL, pronounced the same as Zuul,{{cite book |last1=Holzner |first1=Steven |title=Inside XML |date=2001 |publisher=New Riders |isbn=978-0-7357-1020-7 |page=47 |url=https://books.google.com/books?id=olpC8FqAQpEC&dq=%22XUL%22+%22zuul%22&pg=PA47 |language=en}} made the slogan, "There is no data. There is only XUL!".{{Cite web|url=https://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul|title=Mozilla XML Namespace|website=www.mozilla.org}} The slogan and Zuul as a gatekeeper are referenced in XUL's XML namespace URI and were previously present in all Firefox add-ons:{{cite book |last1=Frederick |first1=Gail |last2=Lal |first2=Rajesh |title=Beginning Smartphone Web Development: Building JavaScript, CSS, HTML and Ajax-based Applications for iPhone, Android, Palm Pre, BlackBerry, Windows Mobile and Nokia S60 |date=15 April 2010 |publisher=Apress |isbn=978-1-4302-2621-5 |page=23 |url=https://books.google.com/books?id=rLqJNQ3_hpsC&dq=%22There+is+no+data.+There+is+only+XUL!%22&pg=PA23 |language=en}}

{{blockquote

|text=http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul

|author=Mozilla

}}

• Glade Interface Designer

{{Reflist|2}}

{{Mozilla projects}}

{{Widget toolkits}}

{{Authority control}}

{{DEFAULTSORT:Xul}}

Category:Mozilla

Category:RDF data access

Category:User interface markup languages

Category:XML-based standards

Category:1997 introductions

Category:Software that uses XUL