Fonte Microsoft:

http://support.microsoft.com/kb/307379/

Overview
XMLDocument is a fundamental building block of the System.Xml class hierarchy. It essentially inherits and extends the XMLNode class, and represents a W3C DOM-compliant XML document in its entirety. Once created or loaded into memory, its contents can be accessed, edited, and manipulated.

Key methods of this class include Load and LoadXml. The former is primarily used to retrieve XML using a resource path, whereas the latter accepts a string value consisting of an XML document or fragment. The InnerText, InnerXml, and OuterXml properties conveniently allow you to retrieve values and XML markup from a document. Below are three examples demonstrating the use of the XMLDocument class.

Overview

The XmlParserContext class allows you to specify context details for the creation of XmlTextReader and XmlValidatingReader objects. Depending on which of the overloaded versions of this class you use, you can assign a number of different context values, including an NameTable, an XmlNamespaceManager, a base URI, xml:lang, xml:space, and an encoding type.

http://www.topxml.com/system_xml/system_xml_xmlparsercontext.asp