User interface markup language

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User interface markup languages describe and render the visual parts of an application. Most are XML-based and rely on a runtime (often a JavaScript engine) to display controls and add interactivity. The idea is to reuse common UI patterns so developers don’t have to code everything from scratch. The markup describes the interface as a tree of elements that the program can build and modify while the app runs.

Examples of UI markup languages:
- HTML: the standard language for web pages, usually used with CSS for styling and JavaScript for behavior.
- XAML: used in Microsoft .NET apps; combines UI, styling, and logic in one XML file.
- QML: part of the Qt framework; describes the UI with JavaScript for behavior and supports hardware acceleration.
- XUL: Mozilla’s UI language for applications using the Gecko engine; works with CSS and JavaScript.
- MXML: XML-based language from the Flex/Adobe ecosystem; compiles to Flash or AIR apps.
- UIML: an open, vendor-neutral standard for UI markup.
- UsiXML: XML language that covers graphical, character, auditory, and multimodal interfaces.
- XFD: XML Form Definition, used in STARLIMS; markup defines forms and is JavaScript-friendly, with HTML5 output in newer versions.
- FXML: XML-based UI definition for JavaFX applications.
- TUIX: used in Tribiq CMS to define and merge user interfaces across plugins.
- OpenLaszlo (LZX): an XML-based UI language with a runtime that originally used Flash, but can run in other environments via Laszlo Legals.
- SVG: a graphics markup language for scalable vector graphics; not a UI language by itself, but often used inside UIs for graphics and can be interactive.
- XFD, HMVCUL, MARIA and others: various XML-based languages for specific platforms or frameworks, each with its own runtime and tooling.

In short, UI markup languages provide a reusable, structured way to describe interfaces, which runtimes render into interactive applications across web, desktop, and mobile platforms.