Markup language

A markup language is a text-encoding system which specifies the structure and formatting of a document and potentially the relationships among its parts. Markup can control the display of a document or enrich its content to facilitate automated processing.

A markup language is a set of rules governing what markup information may be included in a document and how it is combined with the content of the document in a way to facilitate use by humans and computer programs. The idea and terminology evolved from the marking up of paper manuscripts (e.g., with revision instructions by editors), traditionally written with a red pen or blue pencil on authors' manuscripts.

Older markup languages, which typically focus on typesetting and presentation, include troff, TeX, and LaTeX. Scribe and most modern markup languages, such as XML, identify document components (for example headings, paragraphs, and tables), with the expectation that technology, such as stylesheets, will be used to apply formatting or other processing.^{[citation needed]}

Some markup languages, such as the widely used HTML, have pre-defined presentation semantics, meaning that their specifications prescribe some aspects of how to present the structured data on particular media. HTML, like DocBook, Open eBook, JATS, and many others, is based on the markup metalanguages XML and SGML. That is, SGML and XML allow designers to specify particular schemas, which determine which elements, attributes, and other features are permitted, and where.

A key characteristic of most markup languages is that they allow combining markup with content such as text and pictures. For example, if a few words in a sentence need to be emphasized, or identified as a proper name, defined term, or another special item, the markup may be inserted between the characters of the sentence.

The word markup is derived from the traditional publishing practice of marking up a manuscript, which involves adding handwritten annotations in the form of conventional symbolic printer's instructions—in the margins and text of a paper or printed manuscript.

For centuries, this task was done primarily by skilled typographers known as markup men or markers who marked up text to indicate what typeface, style, and size should be applied to each part, and then passed the manuscript to others for typesetting by hand or machine.

The markup was also commonly applied by editors, proofreaders, publishers, and graphic designers, and by authors themselves, all of whom might also mark things such as corrections and changes.