$ perl -MDevel::Peek -e'utf8::upgrade $x="\200\201"; Dump $x; utf8::downgrade $x; Dump $x'
  PV = 0x81623f0 [UTF8 "\x{80}\x{81}"]
  PV = 0x81623f0 "\200\201"\0

##</code><code>##


$ perl -MDevel::Peek -e'utf8::decode $x="\x{2660}"; Dump $x; utf8::encode $x; Dump $x'
  PV = 0x81651c0 [UTF8 "\x{2660}"]
  PV = 0x81651c0 "\342\231\240"\0

##</code><code>##

$ perl -MDevel::Peek -MEncode=_utf8_on,_utf8_off -e'_utf8_on( $x="\200\201" ); Dump $x; _utf8_off $x; Dump $x'
  PV = 0x81651e8 [UTF8 "\x{1}@"]
  PV = 0x81651e8 "\200\201"\0