Correct, I'm referring to the magic added by sv_magic.

$ perl -MDevel::Peek -e'Dump( $1 )'
SV = PVMG(0x561e81adde40) at 0x561e81af86f0
  REFCNT = 1
  FLAGS = (GMG,SMG)                # Has get magic, has set magic
  IV = 0
  NV = 0
  PV = 0
  MAGIC = 0x561e81b067d0           # Magic's data, incl callbacks
    MG_VIRTUAL = &PL_vtbl_sv
    MG_TYPE = PERL_MAGIC_sv(\0)
    MG_OBJ = 0x561e81af86d8
    MG_LEN = 1
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Magic is used by most punctuation vars (e.g. $!, $$, %ENV, %SIG), tie, lvalue operators (specifically substr, vec, pos and $#a), f( $h{ x } ) (to prevent autovivification) and more.