local $_ = "this, (that, those), these ((not enough, (nope)), never), 
+there";
(my $re=$_)=~s/((\()|(\))|.)/${[')','']}[!$3]\Q$1\E${['(','']}[!$2]/gs
+;
$re= join'|',map{quotemeta}eval{/$re/};
die $@ if $@ =~ /unmatched/;
while( /((?:$re|[^,])*)/g ){
    print "$1\n";
}
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