I've investigated the deltas because of
Syntax::Construct and it seemed it had been possible to use recursive subroutines in older Perls, too. 5.10 was just the version that documented the fact.
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]