use Encode;
my ($unicode_string, $utf16_string);

$unicode_string = get_a_unicode_string();

# ^^ this string is a character string internally stored
# as UTF-8

$utf16_string = encode('utf16', $unicode_string);

# ^^ this string is an 'octet' (byte) string internally
# stored as bytes. Each character of the string is stored in
# two bytes of $utf_string.
# (Also note the presence of a UTF-16 BOM)

function_expecting_utf16($utf16_string);


##</code><code>##

$"=$,,$_=q>|\p4<6 8p<M/_|<('=>
.q>.<4-KI<l|2$<6%s!<qn#F<>;$,
.=pack'N*',"@{[unpack'C*',$_]
}"for split/</;$_=$,,y[A-Z a-z]
         {}cd;print lc