VDisplayOverlayMessage - display a 1-bit overlay message.
  VDisplayOverlayMessage(win, ovl, xloc, yloc, msg)
  Window win;
  int ovl;
  int xloc, yloc;
  char *msg;
  VDisplayOverlayMessage display a 1-bit overlay message, at the specified
location in the image window or one of its subwindows. VTurnOnOverlay
should be called earlier to turn on the overlays. 
Return Value
  0 - work successfully.
  6 - invalid window ID.
  223 - message displayed in the image window covered by the dialog window.
  224 - message displayed is out of window boundary.
  225 - no overlay created.
  237 - the overlay does not turn on.
  win - the image window ID or one of its subwindows' ID
  ovl - specifies the overlay number to be used to display the message.
  xloc, yloc - specifies x and y coordinates of the message.
  msg - specifies the message to be displayed.
Side Effects
Entry Conditions
  VTurnOnOverlay should be called first. If the value xloc, yloc, or ovl is 
not valid, msg is NULL, VCreateColormap is not called earlier, or the message 
is totally out of the window boundary, VDisplayOverlayMessage prints an error 
message to the standard error stream, produces a core dump file and exits from
the current process.
Related Functions
VEraseOverlayMessage, VTurnOnOverlay, VTurnOffOverlay, VDisplayImageMessage.