use v5.12;
use warnings;
do './PM.pl';

say for <DATA>

__DATA__
1
2
3

##</code><code>##

<code>
use v5.12;
use warnings;

say for <DATA>

__DATA__
1
2
3
</code>
OUTPUT: <blockquote><i><code>
1

2

3

</code></i></blockquote>

##</code><code>##

use v5.12;
use warnings;

say for <DATA>

__DATA__
1
2
3

##</code><code>##

1

2

3


##</code><code>##

package PM;
use v5.12;
use warnings;
use Scalar::Util qw/openhandle/;

my ($pck) = caller() // __PACKAGE__;

my $data = eval "\\*${pck}::DATA";      # *DATA of caller

my $ctag = "code";                      # avoid messup

local $|=1;

unless ( openhandle($data) ) {

    warn "__DATA__ missing, can't format source code";

} else {

    my $current_pos = tell $data;
    seek $data,0,0;

    say "<$ctag>";

    while ( <$data> ) {
        print unless                      # ignore ...
          /^(do)\s.*PM/                   # . do PM.pl
            or /^__DATA__/ && eof($data); # . __DATA__ on last line
    }

    say "</$ctag>";

    seek $data,$current_pos,0;
}

say "OUTPUT: <blockquote><i><$ctag>";

END { say "</$ctag></i></blockquote>" };

__DATA__