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XML Spy

• XML.GOV -- The website of the US Government's XML Working Group.  Their stated purpose: "The purpose of the XMLWG is to accelerate, facilitate and catalyze the effective and appropriate implementation of XML technology in the information systems and planning of the Federal Government. "
• DII COE XML Registry
• DoD Handbook for Interoperability of Electronic Technical Manuals -- requires PDF reader.

• XML -- W3C XML Resources
• XML.COM -- Information and services for the XML community.
• XML.ORG -- The XML Industry Portal.  Lots of resources.
• The XML Cover Pages -- Resources covering XML, SGML, XSL, XSLT, XPath, XLink, XPointer, HyTime, DSSSL, CSS, SPDL, CGM, ISO-HTML, and others.
• XML 101 -- Huge XML resource portal from Internet.Com.
• XML & Cetus Links -- XML resources at Cetus Links.  Tons of articles, examples, tutorials, etc.  Many resources.
• Sun XML Connection
• XML Directory -- A great starting point for XML resources on the web.
• XML Core -- XML and XSL within Microsoft® MSDN Library.
• GML -- Geography Markup Language at XML.org.  GML is an XML encoding for the transport and storage of geographic information, including both the geometry and properties of geographic features.  Being proposed by the OpenGIS Consortium (OGC).  Access the latest GML Standard at OGC.
• SVG at W3C -- Scalable Vector Graphics at the World Wide Web Consortium.