本文档完整地描述了可扩展标记语言(Extensible Markup Language，XML)，它是标准通用标记语言(Standard Generic Markup Language，SGML)的一个子集。其目的在于使得在Web上能以现有超文本标记语言(Hypertext Markup Language，HTML)的使用方式提供，接收和处理通用的SGML成为可能。XML的设计既考虑了实现的方便性，同时也顾及了与SGML和HTML的互操作性。-integrity of this document describes the Extensible Markup Language (Extensible Markup Language, XML), which is the standard SGML (Standard Generic Markup Language, SGML), a subset. Its purpose is to enable the Web to existing HTML (Hypertext Markup Language, HTML) used to provide, receive and process generic SGML possible. XML design consideration of not only the realization of convenience, but also with regard to the SGML and HTML interoperability.