_LOOKUP_ARGS(<:$2:>, <:$3:>)}} \
$3:>)
-## KV(key, result)
+## KV(key, [result])
##
## Extract the value of the named KEY in the ${extract ...}-style string in
## the current $value (where it may have been left by `LOOKUP-DOMAIN'). The
## RESULT is a pair {IF-FOUND}{IF-NOT-FOUND}; the former may use $value to
## refer to the value; the latter may be `fail' (not in braces) to force
-## expansion failure.
+## expansion failure. The default is to expand to the extracted value or
+## nothing.
m4_define(<:KV:>, <:${extract {$1}{$value}$2}:>)
-## DOMKV(key, result)
+## DOMKV(key, [result])
##
## Extract the value of the named KEY in the ${extract ...}-style string in
## $domain_data; see `KV'.