Sets or gets a value that indicates whether the object is registered as a top-level browser window.
One of the values in the Property Values section.
The architecture of Windows Internet Explorer allows for multiple instances of the IWebBrowser2 object. A "top-level" IWebBrowser2 object is the parent of all other IWebBrowser2 objects. Only top-level objects can register as a browser with this method.
By setting this property to True, Internet Explorer and Windows can locate other top-level IWebBrowser2 objects that can participate in frame name resolution. For example, if the user clicks on a hyperlink that specifies a target attribute that is not in the current window, Internet Explorer searches all registered IWebBrowser2 objects in an attempt to resolve the target name.
After the window is registered as a top-level browser, it cannot be unregistered.