For years surrounding the release Microsoft's Office 2000 the company was applauded in reviews that said Microsoft had changed their spots and were now supporting an open format... XML!

(After all, it was the story MS had spun and reviewers are inherently lazy creatures)

XML is a method for putting structured data into a file. Within this you choose a DTD (Document Type Definition) that defines the rules for holding the specific data you wish to store. The DTD is the unique subset of XML.

If a DTD isn't published it's no more open than a binary file. Although simple examples are quickly disected and analysed - a programmer has great difficulty knowing that when you bold some text it should be written into the file as a <important> rather than a <bold>. If the rules for saving XML structured information are not published and defined, the XML DTD is still a closed standard... despite being XML.

If I were a paranoid man who slept with the door locked, moat full to the brim, then I might claim that MS noticed the XML buzzword hype and wanted to cash in on the goodwill associated with the "open" meta-language. Get in first and spread the unpublished Word2000 DTD as THE STANDARDTM for text documents.