int  initExtern(char ***mime_types, int *nrtypes, float **qual);
  int  openExtern(const W3ADocumentInfo doc,  Widget  area, long id);
 int writeExtern(long id, const char *buf, size_t nchars);
  int  closeExtern(long id);
  int  infoExtern(long id, W3ADocumentInfo *info);
 void eventExtern(long id, long sourceid, long eventtype, void *params);