What is SGML?

From The Gentle Introduction :

``SGML is an international standard for the definition of device-independent, system-independent methods of representing texts in electronic form''

``SGML is a metalanguage, that is, a means of formally describing a language, in this case, a markup language''

• markup (encoding): making explicit an interpretation of text
• markup language: a set of markup conventions used together for encoding texts; it must specify what markup is allowed, what markup is required, how markup is to be distinguished from text, and what the markup means.

The official designation of SGML:

International Organization for Standardization,
ISO 8879: Information processing--Text and office systems--Standard Generalized Markup Language (SGML), ([Geneva]: ISO, 1986).

Hence, SGML is not proprietary .