VS2005 Intellisense support for custom XML Schemas.
I'd love to know how intellisense in Visual Studio 2005 works but all I know, or assume, is it's either based on definitions in a xsd schema (for markup based files) or by reflection of an assemblies metadata (type definitions in code).
I'm looking into WordprocessingML as a means of producing Word 2003 documents for a project I'm working on. There is a fairly comprehensive CHM file for all of Office 2003 schema languages here, Office 2003: XML Reference Schemas. A good thing is the download also includes all the XSD Schema files for the languages, including WordprocessingML.
If you copy these XSD Schemas, or any other schemas you may have, into the C:\Program Files\Microsoft Visual Studio 8\Xml\Schemas directory then Visual Studio's XML editor, when you reference the XSD's namespace, gives intellisense support on the schema.
It's proving useful.