$ perl -E'
   my @hints = ( [refs=>0x2], [subs=>0x200], [vars=>0x400] );
   sub hints {
      my $h = (caller(0))[8];
      my @h = map { $h & $_->[1] ? $_->[0] : () } @hints;
      @h ? join(",", @h) : "[none]"
   }

   say hints;      # [none]
   use strict;
   say hints;      # refs,subs,vars
   {
      say hints;   # refs,subs,vars
      no strict;
      say hints;   # [none]
   }
   say hints;      # refs,subs,vars
'
[none]
refs,subs,vars
refs,subs,vars
[none]
refs,subs,vars