markups

Markups are annotations embedded in text to convey structure, formatting, or other metadata to software. They separate content from how it is presented or interpreted, enabling machines to render, analyze, or convert documents without altering the underlying words.

Markup languages include SGML, XML, HTML, and LaTeX, as well as lighter, human-readable systems such as Markdown. Traditional typesetting and publishing rely on markup for layout and cross-referencing, while modern workflows use markup to enable web display, data interchange, and automated processing. The common feature is the use of tags, elements, or markers that label portions of the text.

There is a distinction among structural markup, which encodes organization (sections, headings, paragraphs); presentation markup, which encodes appearance (bold, italics, spacing); and semantic markup, which conveys meaning (emphasis, citation, date). Contemporary practice emphasizes semantic markup and tends to keep styling in a separate layer, typically a stylesheet, to improve accessibility and reusability.

How markups work varies by format, but generally a document is parsed by software that interprets the tags and renders output such as a web page, a PDF, or a data file. Validity and interoperability are often ensured with schemas, DTDs, or similar constraint mechanisms, and processing can be either document-centric or streaming.

Markup offers machine readability, portability, and clear separation of content from presentation, though it can be verbose and requires tooling. In modern ecosystems, markup underpins the structure of the web, technical documentation, and digital publishing, with ongoing emphasis on semantic clarity and accessible rendering.