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A markup language is a system for annotating a document in a way that is syntactically distinguishable from the text. The idea and terminology evolved from the "''marking up''" of paper manuscripts, i.e., the revision instructions by editors, traditionally written with a blue pencil on authors' manuscripts. In digital media this "blue pencil instruction text" was replaced by tags, that is, instructions are expressed directly by tags or "instruction text encapsulated by tags." Examples include typesetting instructions such as those found in troff, TeX and LaTeX, or structural markers such as XML tags. Markup instructs the software that displays the text to carry out appropriate actions, but is omitted from the version of the text that users see. Some markup languages, such as the widely used HTML, have pre-defined presentation semantics—meaning that their specification prescribes how to present the structured data. Others, such as XML, do not. HyperText Markup Language (HTML), one of the document formats of the World Wide Web, is an instance of SGML (though, strictly, it does not comply with all the rules of SGML), and follows many of the markup conventions used in the publishing industry in the communication of printed work between authors, editors, and printers. ==Types== There are three general categories of electronic markup: ;Presentational markup :The kind of markup used by traditional word-processing systems: binary codes embedded within document text that produce the WYSIWYG effect. Such markup is usually hidden from human users, even authors or editors. ;Procedural markup :Markup is embedded in text and provides instructions for programs that are to process the text. Well-known examples include troff, LaTeX, and PostScript. It is expected that the processor will run through the text from beginning to end, following the instructions as encountered. Text with such markup is often edited with the markup visible and directly manipulated by the author. Popular procedural-markup systems usually include programming constructs, so macros or subroutines can be defined and invoked by name. ;Descriptive markup :Markup is used to label parts of the document rather than to provide specific instructions as to how they should be processed. The objective is to decouple the inherent structure of the document from any particular treatment or rendition of it. Such markup is often described as "semantic". An example of descriptive markup would be HTML's <cite> tag, which is used to label a citation. Descriptive markup -- sometimes called ''logical markup'' or ''conceptual markup'' -- encourages authors to write in a way that describes the material conceptually, rather than visually.〔 Michael Downes. ("TEX and LATEX 2e" ) 〕 There is considerable blurring of the lines between the types of markup. In modern word-processing systems, presentational markup is often saved in descriptive-markup-oriented systems such as XML, and then processed procedurally by implementations. The programming constructs in procedural-markup systems such as TeX may be used to create higher-level markup systems that are more descriptive, such as LaTeX. In recent years, a number of small and largely unstandardized markup languages have been developed to allow authors to create formatted text via web browsers, for use in wikis and web forums. These are sometimes called lightweight markup languages. The markup language used by Wikipedia is one example of such wiki markup. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Markup language」の詳細全文を読む スポンサード リンク
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