# Converts $s to use the UTF8=1 storage format if it's not already.
utf8::upgrade($s);

# Converts $s to use the UTF8=0 storage format if it's not already.
# Dies if it can't.
utf8::downgrade($s);

# Converts $s to use the UTF8=0 storage format if it's not already.
# Returns false if it can't.
utf8::downgrade($s, 1);