$ perl -MDevel::Peek -MEncode=_utf8_on,_utf8_off,encode -e'
    my $x = "\200\201";

    utf8::encode( my $utf8 = $x );
    my $enc = encode("UTF-8", $x);
    _utf8_off( my $off = $x );

    Dump $x;
    Dump $utf8;
    Dump $enc;
    Dump $off;
'
  PV = 0x8165278 "\200\201"\0
  PV = 0x816b608 "\302\200\302\201"\0
  PV = 0x8195050 "\302\200\302\201"\0
  PV = 0x81ff038 "\200\201"\0