An instance of this class should be used as the Engine for wrapper class instances when Excel is available at run-time. If Excel is not available then an emulator engine should be used instead.

An instance is initialized by using either Create()()() or Attach(Object), and must be terminated by calling either Destroy()()() or Detach()()() respectively.

Note that the class is heavyweight if Create()()() is used, since a hidden Excel application instance is created. Care should therefore be taken to create as few as possible instances of the class (preferably only one), and instances should be kept "alive" as long as they are needed.