IsWindowVisible( hWnd ) -> <lVisible>
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 PARAMETER:

  <hWnd>     Is the handle that identifies the target window


 RETURNS:

  <lVisible> is TRUE, if the specified window is visible on the screen 
  (has the WS_VISIBLE style bit set), or FALSE if not.


 DESCRIPTION:

  The IsWindowVisible() function determines the visibility state of the 
  given window. Because the return value reflects the value of the window's
  WS_VISIBLE flag, it may be TRUE even if the window is totally obscured
  by other windows. 
  A window possesses a visibility state indicated by the WS_VISIBLE style
  bit. When this style bit is set, the window is displayed and subsequent
  drawing into the window is displayed as long as the window has the style
  bit set. 
  Any drawing to a window that has the WS_VISIBLE style will not be 
  displayed if the window is covered by other windows or is clipped by its
  parent window. 


 SOURCE:  

  SOURCE\WINAPI\WNDIS.C