Using extra digits in resp.status

In Varnish the .status variables can hold more than three digits, which is useful to send information to vcl_synth{} about which error message to produce:

sub vcl_recv {
   if ([...]) {
       return(synth(12404));
   }
}

sub vcl_synth {
    if (resp.status == 12404) {
        [...]       // this specific 404
    } else if (resp.status % 1000 == 404) {
        [...]       // all other 404's
    }
}