protected function lib_join($args)
{
list($list1, $list2, $sep) = $args;
$list1 = $this->coerceList($list1, " ");
$list2 = $this->coerceList($list2, " ");
$sep = $this->listSeparatorForJoin($list1, $sep);
return array("list", $sep, array_merge($list1[2], $list2[2]));
}