perl -MDevel::Peek -E"$x = chr(129).chr(130).chr(42).chr(131).chr(132); Dump($x); substr( $x, 2, 1 ) = chr(~0); Dump($x); print $x" | od -tx1
SV = PV(0xbadc0) at 0x2c5aa8
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0xb67a8 "\201\202*\203\204"\0
  CUR = 5
  LEN = 8
SV = PVMG(0x2b1078) at 0x2c5aa8
  REFCNT = 2
  FLAGS = (SMG,POK,pPOK,UTF8)
  IV = 0
  NV = 0
  PV = 0x2b3008 "\302\201\302\202\377\200\217\277\277\277\277\277\277\277\277\277\277\302\203\302\204"\0 [UTF8 "\x{81}\x{82}\x{ffffffffffffffff}\x{83}\x{84}"]
  CUR = 21
  LEN = 24
  MAGIC = 0x3177f8
    MG_VIRTUAL = &PL_vtbl_utf8
    MG_TYPE = PERL_MAGIC_utf8(w)
    MG_LEN = -1
Wide character in print at -e line 1.
0000000 c2 81 c2 82 ff 80 8f bf bf bf bf bf bf bf bf bf
0000020 bf c2 83 c2 84
0000025