Hi Petr,

Thanks for catching this. We'll correct it in the next round of
maintenance releases (we're already at release candidate status
for this round).

IMHO the current text is a little unclear, so while we're chaing
it I suggest we change it to this:

diff --git a/bin/nsupdate/nsupdate.c b/bin/nsupdate/nsupdate.c
index 9572fd8..f1cc1b8 100644
--- a/bin/nsupdate/nsupdate.c
+++ b/bin/nsupdate/nsupdate.c
@@ -2146,10 +2146,10 @@ do_next_command(char *cmdline) {
 "zone name                 (set the zone to be updated)\n"
 "class CLASS               (set the zone's DNS class, e.g. IN (default), CH)\n"
 "check-names { on | off }  (enable / disable check-names)\n"
-"[prereq] nxdomain name    (does this name not exist)\n"
-"[prereq] yxdomain name    (does this name exist)\n"
-"[prereq] nxrrset ....     (does this RRset exist)\n"
-"[prereq] yxrrset ....     (does this RRset not exist)\n"
+"[prereq] nxdomain name    (require that this name does not exist)\n"
+"[prereq] yxdomain name    (require that this name exists)\n"
+"[prereq] nxrrset ....     (require that this RRset does not exist)\n"
+"[prereq] yxrrset ....     (require that this RRset exists)\n"
 "[update] add ....         (add the given record to the zone)\n"
 "[update] del[ete] ....    (remove the given record(s) from the zone)\n");