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The XML FAQ — Frequently-Asked Questions about the Extensible Markup Language

Section 1: Basics

Q 1.4: What is SGML?

Standard Generalized Markup Language, ISO 8879:1986

Standard Generalized Markup Language (SGML) (ISO 8879:1986), the international standard for defining markup to describe the structure of different types of electronic document. There is an SGML FAQ from David Megginson at; and Robin Cover's SGML Web pages are at For a brief summary and list of online and print resources, see For a little light relief, try Joe English's ‘Not the SGML FAQ’ at

SGML is very large, powerful, and complex. It was in heavy industrial and commercial use for nearly two decades (and still is, in some places), and there is a significant body of expertise and software that grew up with it, most of which is now available for XML.

XML is a lightweight cut-down version of SGML which keeps enough of its functionality to make it useful but removes all the optional features which made SGML too complex to program for in a Web environment.