STRLEN sublen; /* saved sublen field from rex */
STRLEN suboffset; /* saved suboffset field from rex */
STRLEN subcoffset; /* saved subcoffset field from rex */
+ SV *sv; /* $_ during (?{}) */
MAGIC *pos_magic; /* pos() magic attached to $_ */
SSize_t pos; /* the original value of pos() in pos_magic */
U8 pos_flags; /* flags to be restored; currently only MGf_BYTES*/