'Custom XML' the key to patent suit over Microsoft Word

The short version of the story so many are talking about today: A Texas judge is barring Microsoft from selling Microsoft Word due to alleged patent infringement and fining the Redmondians multiple millions as part of the case.

But most synopses of the case seem to be omitting a key part of the ruling: the concept of "Custom XML."

According to the press release from the lawyers for plaintiff i4i:

"Today's permanent injunction prohibits Microsoft from selling or importing to the United States any Microsoft Word products that have the capability of opening .XML, .DOCX or DOCM files (XML files) containing custom XML."

What is "Custom XML"? Is it a (supposedly) unremovable component of Office (like Internet Explorer is of Windows)?

The first link I found when searching was from the "OOXML is defective by design" site. The 2008 post was born from the politics that continue to swirl around the Office Open XML (OOXML) vs. Open Document Format (ODF) debate. But it still contains some useful information.

First, according to this post, Custom XML is a Word-only thing. It's not part of Excel, PowerPoint or any other Office app.

Post author Stephane Rodriguez links to a couple of Microsoft-provided definitions of Custom XML.

The first, from Office Program Manager Brian Jones, dates back to 2005:

"Custom XML is the support for custom defined schemas. It's that support that allows you truly integrate your documents with business processes and business data. You can define your data using XML Schema syntax, and then you can use that data in your Office documents. By opening up our formats with our reference schemas, and supporting your custom defined schemas, you get true interoperability of your documents."

I did some more searching. I found a 2008 retort to Rodriguez's post that also attempts to define Custom XML. From .Net evangelist Wouter van Vugt:

Custom XML markup "is about embedding custom XML defined outside of Open XML to support solution which aim to structure a document using business semantics, not only using formatting. A great advance since you want to get to the data, and not by saying that the customer name is the 3rd paragraph. The issue is that you cannot just allow any arbitrary XML to be stored in the WordprocessingML package. This would become application specific, and it would break validation since all XML is valid. Not a great idea."

I've seen a couple of bloggers claiming that a prohibition against Custom XML would affect customers working with custom Office templates. From these definitions, it's obvious we're not talking about the simple cover-letter or newsletter formatter that many think of when they hear "template."

Do you expect Microsoft to win its appeal of this case, to settle with i4i? (I'm betting on a settlement, myself.) Do you believe Microsoft could/would "remove" the allegedly infringing Custom XML technology in some way? I'm also still interested in getting more of a layperson's definition of Custom XML -- anyone?

Update: My ZDNet blogging colleague Zack Whittaker managed to get an interesting comment on the case. It sounds like there might be a Plan B, via which Microsoft could disable the Custom XML feature if the company's legal appeal fails. It sounds like Microsoft is not anticipating the case to delay the release of Office 2010. But there is talk of a re-release of Word 2007 with a patch, which the company already has developed, that will disable the Custom XML functionality upon installation.

The "official" Microsoft Legal comment on all this is the much less-detailed one from Microsoft spokesperson Kevin Kutz: "We are disappointed by the court's ruling. We believe the evidence clearly demonstrated that we do not infringe and that the i4i patent is invalid. We will appeal the verdict."