When XUL is non the public standard, it reuses numbers of existent standards & technologies, including CSS, JavaScript, DTD and RDF, which makes it relatively real life to see for humans by using the background around web programming & project.

the independent profit of XUL is that it will bring a elementary & personal definition of most common widgets. This reduces a software development effort in how else correspondent to the cost offered by 4GL tools.

Introduction
An XUL interface is occasionally defined when triplet distinct sets of components: Content: A XUL documents, which define a layout of the interface. Skin: A CSS & image files, which define a appearance of an application. Locale: A DTD documents, which define entities for easy software localization.

For an lesson, watch a "Hello World!" program written in XUL.

XUL elements
XUL defines the wide range of elements, which about belong to the ensuing types: ; Top-level elements: e.g. window, page, dialog, wizard, etc. ; Widgets : e.g. label, button, text box, list pack, combo box, radio button, check box, tree, menu, toolbar, group pack, tab box, color picker, spacer, splitter, etc. ; Pack model: e.g. pack, grid, fold, deck, etc. ; Cases & Scripts: e.g. script, command, key, broadcaster, observer, etc. ; Information source: e.g. templet, rule, etc. ; Others: e.g. overlayer (correspondent to SSI, but client side & sir thomas more mighty), iframe, web browser, editor, etc.

These are imaginable to utilise elements from either more applications of XML in XUL documents, like XHTML, SVG, and MathML.

Occasionally most common widgets - like spinbox, slider, & canvas - come non available in the todays XUL widget placed, however are planned for XUL Two.Cypher [http://wiki.mozilla.org/wiki/XUL:Home_Page].

Usage
When XUL is mostly utilized for creating a Mozilla application itself & its extensions, these are conceivable to let it run for web applications transferred over HTTP. One of a virtually all easily-known XUL applications of this nature and severity is the Mozilla Amazon Browser, which provides the rich interface for looking books at Amazon.com. Yet, several of the mighty features of Mozilla, prefer privileged XPCOM objects, are not available to unpriviledged XUL documents (unless a script is digitally signed), & such documents likewise suffer from either various limitations of a web browser, like the inability to bucket remote XUL, DTD and RDF documents.

Film references
A XUL title occurs as information to the film Ghostbusters, in which a ghost of an ancient Sumerian deity known as Zuul possesses a character Dana Barrett (played by Sigourney Weaver) and declares "There is no Dana, only Zuul". Since XUL is unusual in XML to define an interface, like than a document, its developers adopted the catchword "There is no data, only XUL". This is referred to per XML namespace URI at the beginning of each XUL document, http://www.mozilla.org/keymaster/gatekeeper/there.is.exclusively.xul; whenever viewed by using a XUL-capable application, a document pointed to displays the shibboleth around big letters in the center of the screen (similar thereto to the correct).

"Keymaster" & "gatekeeper" come besides information to the equivalent plotline. This is non a just information to Ghostbusters in Mozilla - sometimes, a JavaScript debugger component is called Venkman, one of the independent characters in the film.