I've blogged a few times about the support for custom defined schema in the OpenXML formats. (http://blogs.msdn.com/brian_jones/archive/tags/Custom+Schema+Solutions/default.aspx)

I've had a few folks ask me if there are similarities between the custom defined schema support and Microformats. While the approach is a bit different, the scenarios are very similar. The key is that you want to take documents stored in a presentation based format (HTML, OpenXML, ODF), and add additional information that helps describe the actual meaning of the data. This makes it much easier to search for, reuse, and modify the data within a document. Doug Mahugh has a great post that talks about how you could take some of the microformat schemas out there and apply them to an office document using the custom XML support. Take a look: http://blogs.msdn.com/dmahugh/archive/2007/03/03/microformats-and-open-xml.aspx

The added benefit of the custom xml support tied to content controls is that you can program against just the data and not interact with the display markup at all if you choose. I had a couple screencasts where I demo'd how this works:

• Operating against your data rather than Word's data – In this screencast I give a quick demo of the benefit you have as a developer / solution builder when you map your data to the content controls within a document.
• Moving custom XML data from Excel to Word – In this screencast I show how you can use the custom XML support in Word and Excel to move your own data between the two applications. Rather than the basic copy/paste type functionality where you move the content and presentation, in this example I use Excel to run a model against my data and pull together some results. I then take the results out of the table in Excel and present them in a completely different format in Word.

-Brian