XML, DTD, XSL, XHTML

XML : eXtensible Markup Language
http://www.w3schools.com/xml/

Data Type Definition
http://www.w3schools.com/dtd/

XSL : eXtensible Stylesheet Language
http://www.w3schools.com/xsl/

XML Schema
http://www.w3schools.com/schema/

Xpath
http://www.w3schools.com/xpath/

XSL-FO
http://www.w3schools.com/xslfo/

XML DOM : XML Document Object Model
http://www.w3schools.com/dom/

XHTML
http://www.w3schools.com/xhtml/
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http://www.w3schools.com/ 이 여러 프로토콜들을 아주 쉽게 설명해 놓은 것 같다.
표준문서처럼 어렵지 않고 tutorial처럼 쉽다.

XML Data type in ADO.Net v2.0 - Part I
http://blogs.msdn.com/sushilc/archive/2004/07/29/201042.aspx