my @extvars = qw(sv_undef sv_yes sv_no na dowarn
curcop compiling
tainting tainted stack_base stack_sp sv_arenaroot
+ no_modify
curstash DBsub DBsingle debstash
rsfp
stdingv
study_chunk
add_data
re_croak2
+ regpposixcc
regmatch
regrepeat
regrepeat_hard
regcppop
regcp_set_to
cache_re
+ restore_pos
reghop
reghopmaybe
dump