The error function

seal_error ()
       Displays an error message on the screen. This function is a pointer 
       to an error function. You may redirect it to your own function, but 
       it's better to leave it unchanged. 

       l_int  (*seal_error) ( l_int errtype, l_text str, ... );

       errtype     The type of error to display. These are supported in Seal 1.0:

                      ERR_NOTHING     - No error has occured.
                      ERR_NONREGULAR  - This is a very serious error.
                      ERR_INFO        - This is not so serious. Just inform the
                                        user that an error has occured.

       str         Contains the formatted text to display. Supports the same
                   formatting as the "printf()" function.
       ...         Other strings and variables to show in text.