chomp( (undef, $_, undef, @words) = <> );

%restore_case = map { lc, $_ } @words;

$list = join '|', map { scalar reverse lc } @words;

m/^ (?: ($list | $ | (?{ pop @submatches }) (?!) ) 
(?{ push @submatches, $^N }) )+ $/x;

pop @submatches;

print join ' ', map { $restore_case{ scalar reverse } } @submatches

##</code><code>##

m/^ 
	(?: 
		( $list  # dictionary joined with '|'
			| $  # if end of line then success, so don't pop array
			| (?{ pop @submatches }) (?!)  # pop array and suddenly fail
		) 
		(?{ push @submatches, $^N })  # after every matched word, push it to array
		# $^N - last captured group
	)+ 
$/x;

##</code><code>##

":aa2bb4cc6dd8" =~ / (:)
                     (?{ [] })   # initialize $^R
                     (?:
                         (\w\w) (\d)
                         
                         # add captures to $^R:
                         (?{ [@{$^R}, [$2, $3]] })
                     )*
                   /x;

##</code><code>##

my @R;
":aa2bb4cc6dd8" =~ / (:)
                     (?:
                         (\w\w) (\d)
                         
                         (?{ push @R, [$2, $3] })
                     )*
                   /x;

##</code><code>##

use Data::Dumper;
sub dd { print Dumper(shift) };

("aa2bb4cc6dd8" x 1e3) =~ /
                     (?{ [] })   # initialize $^R
                     (?:
                         (\w\w) (\d)
                         
                         # add captures to $^R:
                         (?{ [@{$^R}, [$1, $2]] })
                     )*
                   /x;
                   
dd @{ $^R }[ -1 ]

##</code><code>##

use Data::Dumper;
sub dd { print Dumper(shift) };

my @R = ();

("aa2bb4cc6dd8" x 5e3) =~ /
                     (?:
                         (\w\w) (\d)
                         
                         # push captures to @R:
                         (?{ push @R, [$1, $2] })
                     )*
                   /x;
                   
dd @R[ -1 ]

##</code><code>##

$VAR1 = [
          'dd',
          '8'
        ];