GUID and ProgID Information
This section contains version-specific GUID and ProgID information for all current versions of Microsoft® XML Core Services (MSXML), formerly known as the Microsoft XML Parser.
MSXML version 3.0 was the last version of MSXML to support version-independent GUIDs and ProgIDs. Starting with version 4.0, MSXML is installed on your computer in side-by-side mode. This means that, for example, installing MSXML 5.0 for Microsoft Office Applications does not replace any previously installed version of the MSXML parser on your computer. This is done to protect the quality of applications that are currently using earlier versions of MSXML. Side-by-side mode also allows you to decide which version of the parser to use in your code.
After you install MSXML 4.0 or later, applications that use version-independent ProgIDs continue to run MSXML 3.0 in all currently supported versions of Windows. To use version 4.0 or later, however, applications must be written to use the appropriate version-dependent class IDs (CLSIDs) and ProgIDs that reference the appropriate DLL (Msxml4.dll, Msxml5.dll, Msxml6.dll and so on).
This ensures stability in your applications. It also enables customers to implement new and improved versioning solutions by using the side-by-side installation technology provided with Windows.