Defines the types (or classes) of documents and the properties associated with those types. This field reads the Windows registry base key HKEY_CLASSES_ROOT.
Both conventional applications and OLE applications use data that is stored under this key. This key also provides backward compatibility with the Windows 3.1 registration database by storing information for DDE and OLE support. File viewers and user interface extensions store their OLE class identifiers in this key, and processing servers are registered in this key.