>perl -MDevel::Peek -e"utf8::upgrade( $x = "abc" ); Dump($x); length($x); Dump($x);"
SV = PV(0x7b8d54) at 0x328554
  REFCNT = 1
  FLAGS = (POK,pPOK,UTF8)
  PV = 0x7b9fac "abc"\0 [UTF8 "abc"]
  CUR = 3
  LEN = 12
SV = PVMG(0x31e8e4) at 0x328554
  REFCNT = 1
  FLAGS = (SMG,POK,pPOK,UTF8)
  IV = 0
  NV = 0
  PV = 0x7b9fac "abc"\0 [UTF8 "abc"]
  CUR = 3
  LEN = 12
  MAGIC = 0x31f17c
    MG_VIRTUAL = &PL_vtbl_utf8
    MG_TYPE = PERL_MAGIC_utf8(w)
    MG_LEN = 3