本文件含五个XML课件，关于XML的基础知识，SCHEMA的相关介绍和学习，XML模式，DTD-This document contains five XML courseware, XML, basic knowledge about, SCHEMA related to introduction and learning, XML models, DTD

这个是一个DTD教程，DTD是一种XML文件的文档模式文件，它描述了XML文件内部应有的格式。-This is a DTD tutorial, DTD is an XML file document schema file, which describes the XML file inside proper format.