Used to link .NET forms to Excel.
                class WinWrapper  | 
            
          The WinWrapper class establishes a link between a Windows API window handle
          (HWND) and
          the .NET runtime Forms classes.
          In order to show a modal dialog during an add-in function
          (or during an add-in library event handler),
          you can construct a WinWrapper to use as the parent of your own window.
        WinWrapper implements the IWin32Window interface,
      and can be used wherever .NET expects a window handle, as in the 
      example C++/CLI code below.
      
HWND hwndOwner;
System::Windows::Forms::MessageBox::Show(
    gcnew XllPlus::Forms::WinWrapper(hwndOwner), 
    "Hello from .NET");
      Header: xlpclrforms.h