This property contains a read-only reference to a JavaPackage that sits at the top of the Java package hierarchy, the root node of the tree. A JavaPackage is a container for other JavaPackage objects and JavaClass objects. By default, the Netscape Navigator browser will have three packages belonging to this top-level node (java, sun, and Netscape), and these will contain other packages. There may be additional externally-supplied packages over and above these three default items.
It is understandable that Microsoft does not go very far with support for Java other than being able to run a Java applet. There is no access to Java packages directly from script in the same way. You can run a Java Applet and interact with that, but its not quite the same thing.