SGML is an acronym for Standard Generalized Markup Language. This language was developed and organized by the International Organization for Standards in 1986 as a means for organizing and identifying elements of a document that are destined to be formatted. The identification process is termed marking up. To markup a document is to indicate with symbols or code how a particular piece of text should be formatted; that is, what its appearance will be in the final version. For example, in a word processing document text can be formatted with respect to font, alignment and size, among others considerations.

SGML can also be described as a metalanguage—a means of formally describing a language. As a markup language, SGML specifies what markup is allowed, what markup is required, and how the markup will be distinguished from text. The meaning of...