User interface markup language

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A user interface markup language is a markup language that renders and describes graphical user interfaces and controls. Many of these markup languages are dialects of XML and are dependent upon a pre-existing scripting language engine, usually a JavaScript engine, for rendering of controls and extra scriptability.

The concept of the user interface markup languages is primarily based upon the desire to prevent the "re-invention of the wheel" in the design, development and function of a user interface; such re-invention comes in the form of coding a script for the entire user interface. The typical user interface markup language solidifies often re-used program or script code in the form of markup, making it easier to focus upon design of a user interface in an understandable dialect as opposed to focus on function.

User interface markup languages, like most markup and programming languages, rely upon sub-application runtimes to interpret and render the markup code as program code that can be processed and put out in the desired form. In XML-based user interface markup languages, the markup is usually interpreted and represented as a tree of nodes that may be manipulated at runtime by the application's code or dynamically loaded user script.