7-bit ISO-8859-1 (also called "ASCII" {grin}) is a proper subset of UTF-8, but not 8-bit ISO-8859-1. So yes, you'd need to declare the file as ISO-8859-1 if you wanted to have any "second half" characters, but otherwise you can let it default to UTF-8.

-- Randal L. Schwartz, Perl hacker