Yes, it's quite possible. You can save a Word document as XML to see the WordProcessingML Word generates, but when creating a document you don't need all of that.
Word's XML vocabulary - WordProcessingML - is documented on microsoft.com. "Office 2003 XML" from O'Reilly discusses quite a few of the ins-and-outs, and tells you exactly what you do need in order to generate a document Word 2003 can interpret correctly.
-- Cindy Meister (Word MVP) |