#define SV_CONST_RETURN 32
#define SV_MUTABLE_RETURN 64
#define SV_SMAGIC 128
+#define SV_HAS_TRAILING_NUL 256
#define sv_unref(sv) sv_unref_flags(sv, 0)
#define sv_force_normal(sv) sv_force_normal_flags(sv, 0)
+#define sv_usepvn(sv, p, l) sv_usepvn_flags(sv, p, l, 0)
+#define sv_usepvn_mg(sv, p, l) sv_usepvn_flags(sv, p, l, SV_SMAGIC)
/* We are about to replace the SV's current value. So if it's copy on write
we need to normalise it. Use the SV_COW_DROP_PV flag hint to say that