questions about encode/decode

Just a couple of questions:

1. What is the result of Encode::encode("iso-8559-1", $x) if $x is not
a utf8 string (i.e. Encode::is_utf8($x) returns false.)

2. What is the result of $string = decode("iso-8859-1", $octets) if
$octets is a utf8 string?

Thanks!