markup

Markup is a system for annotating a digital document to describe its structure, presentation, or semantics while keeping the content readable. A markup language uses symbols, tags, or commands to mark regions such as headings, paragraphs, lists, or emphasis, enabling software to render or process the document accordingly.

Historically, markup evolved from typesetting and early document preparation systems. SGML, standardized in the 1980s, provided a framework for describing document structure. HTML, developed for the World Wide Web in the 1990s, defines a fixed set of elements for web pages. XML, designed as a flexible data-exchange format, refined SGML concepts. Lightweight markup languages such as Markdown and reStructuredText appeared later to emphasize human readability, while TeX and LaTeX offer extensive markup for high-quality typesetting.

Markup languages vary in syntax but share a common goal: describe structure rather than dictate appearance. In HTML, markup consists of tags like <p>, <h1>, and <ul> with attributes; in XML, elements and attributes convey data structure; in Markdown, simple punctuation indicates headings, lists, and emphasis; in LaTeX, commands such as \section and \emph mark sections and emphasis.

Presentational markup concentrates on how content looks, while semantic markup aims to convey what content means. Modern practice often separates structure from style using CSS or style sheets, keeping markup focused on semantics and data, while presentation details are applied during rendering.

Markup plays a central role in web pages, documentation, data interchange, and publishing workflows. It supports automated processing, searchability, accessibility, and machine readability, reflecting a long-standing design principle of treating content and presentation as distinct concerns.