Microsoft has pages out now which detail the extensions to OOXML they are using in Office 2010.
OOXML is an extensible format, with a feature called Markup Capability and Extensibility to allow better management of extensions, in particular signalling whether there are alternative media versions available and whether the extension elements can be treated as decorative throwaways or information that an OOXML consumer must utilize.
You can see overviews or details here for:
It would be consistent if the ISO standard for OOXML included this information, at some stage, in some form. MCE allows a kind of nice layering, by time, for evolving standards: I think it is a real mistake in ODF 1.2 not to adopt MCE also, just for future-proofing: it makes older applications more robust in the face of newer format versions as well as vice versa.
Without such a mechanism for practical modularity, standards groups get trapped in the big rut of major releases, even for minor features. It discriminates against niche requirements and goes against agility and innovation. To a great extent, ODF without MCE is a white flag of surrender by the ODF TC: that the basic shape and feature set of office suites will be set by Microsoft, and ODF will re-implement them in some neater way that fits in with the FOSS platforms. Perhaps it is just realistic, but sorry it seems like corporatist thinking.
Why so much emphasis on Backstage?
This section also has some Office 2010 XML formats you wouldn't expect to see in ISO OOXML: for example, the XML formats for making custom user interfaces. I like XUIs: we had great success using SwiXML for Java, a decade ago. Glancing through these formats, the one that caught my eye was the customizations for Backstage, which is the name Microsoft give to the highly enhanced document properties box.
Actually, it seems Backstage is concerned with all aspects of a document that don't relate directly to things you see on the page WYSIWYG, which are taken care of by direct manipulation and the Ribbon interface: what Clay Satterfield calls OUT features.
Satterfield says (of the Office team working on the Office 2007 feature set and concentrating on the IN features):
What we were sorely lacking was the WYSIWYG equivalent for the OUT features.
What made this particularly scary for us internally is that for the foreseeable future, the OUT features are the ones that are growing rapidly. Documents are now rarely simple files authored by one person who keeps it on his hard drive until he prints. Collaboration and sharing are critical. Documents are key parts of complicated business processes. There's a ton of context surrounding documents, and increasingly, that context needs to surface within the authoring application.
My company Topologi's old Collaborative Markup Editor allowed you to check things like who was editing which document, which directories they have edited in recently, to send documents on a whiteboard arrangement to deal with issues, and to chat, based on a peer-to-peer system.
I think it is the way that things will go, eventually. It is not just the document that we need to share or see, it is also work histories, actual window screenshots, notes, and so on. Automatic peer-to-peer systems provide a kind of zero-configuration way to allow this.
So I am quite intrigued by Backstage. I tend to see it as a reversal of the usual sales pitch: instead of "Buy our application: it can add value to your existing backend" it is "Buy our backend: it can add value to your existing office suite."