libbind ns_sign() and ns_verify() parameter in_timesigned not documented

[Stacey Jonathan Marshall]

The tsig manual page description for ns_sign() and ns_verify() include a 
parameter named in_timesigned of type time_t.  However there is no 
description of this parameter as there is for the others:

$ less libbind-6.0/doc/tsig.cat3
TSIG                                 LOCAL                                TSIG

NAME
     ns_sign, ns_sign_tcp, ns_sign_tcp_init, ns_verify, ns_verify_tcp,
     ns_verify_tcp_init, ns_find_tsig -- TSIG system

SYNOPSIS
     int
     ns_sign(u_char *msg, int *msglen, int msgsize, int error, void *k,
         const u_char *querysig, int querysiglen, u_char *sig, int *siglen,
         time_t in_timesigned);

...
     int
     ns_verify(u_char *msg, int *msglen, void *k, const u_char *querysig,
         int querysiglen, u_char *sig, int *siglen, time_t in_timesigned,
         int nostrip);


 From a cursory review it does not seem to be used unless error == 
ns_r_badtime.
Could someone describe the purpose of parameter? 

Regards,  Stacey