It works! I had some trouble figuring out how to implement it, because with 'use strict' the recursive RegEx stays undefined.

#!/usr/bin/perl -w
use strict;
my $input = "aa (bb cc) dd (ee (ff (gg) hh) jj) kk ((ll)) mm";
no strict 'vars';
# from $RE{balanced}{-parens=>'()'};
$REparens = qr/
    (?:(?:(?:[(](?:(?>[^)(]+)
    |(??{$REparens}))*[)]))
    |(?:(?!)))/x;

my $re = $REparens;    
use strict;

print "input: $input\n";
while ($input =~ /\G(\w+|$re)\s*/gc) {
    print "$1\n"
}
__END__
output:
aa
(bb cc)
dd
(ee (ff (gg) hh) jj)
kk
((ll))
mm
[download]

Making a block of no strict 'vars' solves the problem. There I can assign the recursive regex to a proper ly declared variable, or call explicitly ($main::REparens).
Thanks a million.

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