Provides the URL of the object's implementation. In Internet Explorer, the URL can point to the client computer's CLSID directory (with a clsid: URL) that stores all the IDs for registered ActiveX controls, such as DirectX or Media Player. IE 4 for Macintosh names this property classID, but the name was repaired to all lowercase in IE 4.5. The W3C DOM omits this property, even though HTML 4 includes the corresponding attribute.