C# Definition:

    public interface IContextMenu3 : IContextMenu2 {
        [PreserveSig] int HandleMenuMsg2( uint uMsg, uint wParam, uint lParam, IntPtr plResult );
    }

VB Definition:

<ComImport> _
<Guid("TODO")> _
'TODO: Insert <InterfaceType(ComInterfaceType.InterfaceIsIUnknown)> _ if this doesn't derive from IDispatch
Interface IContextMenu3
   TODO
End Interface

User-Defined Types:

None.

Notes:

Make sure your object explicitly lists all the IContextMenu interfaces or the shell may never call IContextMenu3.HandleMenuMsg2. For example:

public class ContextMenuHandler : IShellExtInit, IContextMenu, IContextMenu2, IContextMenu3

{

  // ...
  // implementation
  // ...

}