Word's XML features

WordprocessingML WordprocessingML, a markup vocabulary representing the content and all the details of Microsoft Word documents, is at the heart of Word's XML features. Users may never encounter WordprocessingML directly, and Microsoft has spent a lot of effort promoting the other XML features in Word, but a basic understanding of WordprocessingML is necessary to create Word XML solutions of any flavor.
XSLT XSLT transformations are the other critical ingredient of Word's XML support, as XSLT serves as the buffer between Word's own data structures and those of the rest of the world.
W3C XML Schemas - XSD Developers who want to use Word to edit their own custom vocabularies will need to use W3C XML Schema, or at least find a tool for creating these schemas. Word uses schemas to specify the markup available to users at any given point in a document.
A new markup interface The task pane provides users who are creating markup with access to their schemas.