pascal void modernEventProc(NavEventCallbackMessage callBackSelector,
                            NavCBRecPtr callBackParms, void* callBackUD)
  {
  ...
  switch(callBackSelector)
    {
    ...
    case kNavCBStart:
      {
      OSStatus theStatus = noErr;
      AEDesc theLocation = {typeNull, NULL);
      FSSpec theFSSpec;
      theStatus = FSMakeFSSpec(...<your construction here>..., &theFSSpec);
      if (theStatus != noErr) {... your error handling here ...}
      theStatus = AECreateDesc(typeFSS, &theFSSpec, sizeof(FSSpec), &theLocation));
      if (theStatus != noErr) {... your error handling here ...}
      theStatus = NavCustomControl(callBackParms->context,
                        kNavCtlSetLocation, (void*)&theLocation);
      if (theStatus != noErr) {... your error handling here ...}
      }
    ...
    }
  ...
  }

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