The Hyper Text Markup Language (HTML) is mainly used for writing web pages. It is XML based and allows users to create structured text documents (by using tags and attributes) and insert text semantics (paragraphs, headers, tables, etc.).

Usually it is used in conjuncture with JavaScript - which influences the behaviour of browsers - and CSS (Cascading Style Sheets) - for formating text and overall page appearance.

Latest standard release by W3C was that of HTML 5.0 (ISO/IEC 15445:2000) in October 2014.

In 2008 a draft for an HTML 5 was released. It includes several modifications:

• obsolete tags such as font, frameset or center were removed
• new tags such as footer, audio, video, nav, etc.
• new attributes such as ping, async, etc.
• new parsing mechanism
• ability to use SVG and MathML in text/html
• etc.

Related languages include the XHTML 1.1 which is an extension of HTML based on XML and not SGML.

Three sub-specifications exist for both HTML and XHTML:

• Strict: represents the standard proper and encourages the omission of presentational markup (eg. center or font tags) by using style sheets (CSS)
• Transitional: allows for presentational markup
• Frameset: allows for presentational markup and additionally from Transitional a frameset replacing body, containing frame elements, and optionally noframes, with a body

Each document is checked against a DTD (Document Type Definition) file for validity.