... This handle is used to identify the file in subsequent calls to other DAF routines. ... Exceptions 1) If the specified file has already been opened, either by the DAF routines or by other code, an error is signaled by routines in the call tree of this routine. ... 4) If the specified file is not a DAF file, an error is signaled by routines in the call tree of this routine. ... 7) If an I/O error occurs in the process of opening the file, routines in the call tree of this routine signal an error. ...