$ perl -Mv5.14 -e'use utf8; sub fée { }'

$ perl -Mv5.14 -e'no utf8; sub fée { }'
Illegal declaration of subroutine main::f at -e line 1.

##</code><code>##

$ perl -Mv5.14 -e'
   binmode STDOUT, ":encoding(UTF-8)";
   $_ = "\xE9"; utf8::upgrade($_); say;
' | od -t x1
0000000 c3 a9 0a
0000003

$ perl -Mv5.14 -e'
   binmode STDOUT, ":encoding(UTF-8)";
   $_ = "\xE9"; utf8::downgrade($_); say;
' | od -t x1
0000000 c3 a9 0a
0000003