HTML: HyperText Markup Language

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An example of a very basic document in HTML, with a title and body text

The HyperText Markup Language, or HTML, is the building block of the Web. It uses markup to annotate text, images, and other content for display and is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets and scripting languages such as JavaScript.

HTML markup includes special "elements" such as

<head>, <title>, <body>, <header>, <footer>, <article>, <section>, <p>, <div>, <span>, <img>, <aside>, <audio>, <canvas>, <datalist>, <details>, <embed>, <nav>, <output>, <progress>, <video>, <ul>, <ol>, <li> 

and many others.

An HTML element is set off from other text in a document by "tags", which consist of the element name surrounded by "<" and ">". The name of an element inside a tag is case insensitive. That is, it can be written in uppercase, lowercase, or a mixture. For example, the <title> tag can be written as <Title>, <TITLE>, or in any other way.

HTML also has a Document Object Model, which is an interface that treats an HTML document as a tree structure, with each node defined as an object. DOM methods (e.g. with JavaScript) use access to the objects in this tree to change their structure, style or content. Objects have event handlers, which execute after an event (such as a mouse click) happens.

A basic Document Object Model (DOM) tree:

Document Object Model (DOM) tree