# in some parent formatting, template processing module
use Template;   # not actually using it in the code here
use Template::Stash;
$Template::Stash::LIST_OPS->{ serial } =
    sub {
        my @list = @{ +shift || [] };
        join(', ', @list[0..$#list-1]) .
            (@list>2 ? ',':'' ) .
            (@list>1 ? (' and ' . $list[-1]) : $list[-1]);
    };