Cocoa provides views that are either not currently available in HIToolbox or are available without full support. These include views such as WebView, PDFView, QTMovieView, and NSTokenField. In addition, the Cocoa and Carbon control hierarchies are incompatible, so it has been difficult or impossible to have views from both frameworks embedded within the same window.
A new type of HIView called HICocoaView provides a general solution to these problems. You can embed a Cocoa view (any subclass of NSView) inside the HIView control hierarchy of a Carbon window. This is accomplished by associating the Cocoa view with a Carbon wrapper view called HICocoaView, a subclass of HIView. You can use standard HIView functions to manipulate the wrapper view, and you can use Cocoa methods to manipulate the associated Cocoa view. HICocoaView is supported only in compositing windows.
HICocoaView is available in Mac OS X v10.5 and later. For more information, see Carbon-Cocoa Integration Guide.