Specifies the following: (a) an abstract syntax known as the Standard Generalized Markup Language (SGML). The language expresses the description of a document's structure and other attributes, as well as other information that makes the markup interpretable; (b) a reference concrete syntax that binds the abstract syntax to specific characters and numerical values, and criteria for defining variant concrete syntaxes, and (c) conforming documents in terms of their use of components of the language and systems in terms of their ability to process conforming documents and to recognize markup errors in them. The Standard also specifies how data such as images, graphics, or formatted text (not defined by the Standard) can be included in a conforming document. This Standard is identical with and reproduced from ISO 8879:1986.