To show TIMTOWTDI, I tried to play with a dynamic dispatch table:

#!/usr/bin/perl
use strict;
use warnings;

my @dd = qw/AA JJ CC M 1 1 3 4 D JJ 1 1 D M 3 3 4 D C M 3 3 3 D P Z/;
my @results;

my %dispatch = ( M => \&start );

sub empty {}
sub store { push @{ $results[-1] }, $_ }
sub start {
    %dispatch = ( D => \&stop );
    push @results, [];  # Start a new group.
    return \&store      # Store the next elements.
}
sub stop {
    %dispatch = ( M => \&start );
    store();
    return \&empty      # Stop storing the elements.
}

my $on_each = \∅

for (@dd) {
    my $change = $dispatch{$_};
    $on_each = $change->($_) if $change;
    $on_each->($_);
}

use Data::Dumper;
print Dumper \@results;
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($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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