[vtkusers] "class" at the top

[Louis Desjardins]

Hi,
Im creating my own class derived from vtkIneractorStyle adn I am just 
looking at vtkInteractorStyleFlight.cxx as an example

The first few lines of code are:

00057 #ifndef __vtkInteractorStyleFlight_h
00058 #define __vtkInteractorStyleFlight_h
00059
00060 #include "vtkInteractorStyle.h"
00061 class vtkCamera;
00062 class vtkPerspectiveTransform;
00063 //BTX
00064 class CPIDControl;
00065 //ETX
00066
00067 class VTK_RENDERING_EXPORT vtkInteractorStyleFlight : public 
vtkInteractorStyle

What do lines 61 and 62 mean?? I've never really seen that syntax.. And 
would I need to have these lines in my derived class?
Thank you!

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