use Devel::Peek qw[ Dump ];;
Dump \substr 'fred', 1, 2;;

SV = RV(0x78148) at 0x78138
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x3d39898
  SV = PVLV(0xf3758) at 0x3d39898
    REFCNT = 2
    FLAGS = (PADMY,GMG,SMG,pPOK)
    IV = 0
    NV = 0
    PV = 0x3e5eda8 "re"\0
    CUR = 2
    LEN = 8
    MAGIC = 0x3e75af8
      MG_VIRTUAL = &PL_vtbl_substr
      MG_TYPE = PERL_MAGIC_substr(x)
    TYPE = x
    TARGOFF = 1
    TARGLEN = 2
    TARG = 0x3d39f58
    SV = PV(0x3e25950) at 0x3d39f58
      REFCNT = 2
      FLAGS = (PADTMP,POK,READONLY,pPOK)
      PV = 0x3e5ece8 "fred"\0
      CUR = 4
      LEN = 8