What is the .MSPX file extension?

A few internet searches led me to http://www.microsoft.com/backstage/bkst_column_46.mspx, but it was a dead link. Fortunately, it was archived on the Wayback Machine and you can read it here:

http://web.archive.org/web/20040803120105/http://www.microsoft.com/backstage/bkst_column_46.mspx

The .MSPX extension is part of the "Microsoft Network Project," which according to the article above, is designed to give Microsoft's sites a consistent look-and-feel worldwide, as well as keep the design of the site seperate from the content. Here's the gist of the article:

The presentation framework includes a custom Web handler built in ASP.NET. Pages that use the presentation framework have the .mspx filename extension, which is registered in Microsoft Internet Information Services (IIS) on the Web servers. When one of the Microsoft.com Web servers receives a request for an .mspx page, this custom Web handler intercepts that call and passes it to the framework for processing.

The framework first checks to see whether the result is cached. If it is, the page is rendered immediately. If the page is not cached, the handler looks up the URL for that page in the table of contents provided by the site owner (see below) to determine where the XML content for the page is stored. The framework then checks to see if the XML is cached, and either returns the cached content or retrieves the XML from the data store identified in the table of contents file.

Within the file that holds the content for the page, XML tags identify the content template to be used. The framework retrieves the appropriate template and uses a series of XSLTs to assemble the page, including the masthead, the footer, and the primary navigational column, finally rendering the content within the content pane.

I think it's an XML based template system that outputs HTML. I think it's internal to MS only.

Well, a little googling found this:

The presentation framework includes a custom Web handler built in ASP.NET. Pages that use the presentation framework have the .mspx filename extension, which is registered in Microsoft Internet Information Services (IIS) on the Web servers. When one of the Microsoft.com Web servers receives a request for an .mspx page, this custom Web handler intercepts that call and passes it to the framework for processing."

I'd like to find out more info though.