my $str = <<TEXT;
STARTP
TITLE
some gibberish
some more gibberish
ENDTITLE
TITLE
some gibberish
some more gibberish
ENDTITLE
TITLE
some gibberish
some more gibberish
ENDTITLE
ENDP
STARTP
TITLE
some gibberish
some more gibberish
ENDTITLE
TITLE
some gibberish
some more gibberish
ENDTITLE
TITLE
some gibberish
some more gibberish
ENDTITLE
ENDP
TEXT

my @ary;
foreach my $p ($str =~ /^STARTP\n(.*?)ENDP/msg) {
    my @p;
    foreach my $t ($p =~ /^TITLE\n(.*?)ENDTITLE/msg) {
        
        push @p, $t;
    }
    push @ary, \@p;
}
use Data::Dumper;
print Dumper(\@ary);
[download]

$VAR1 = [
          [
            'some gibberish
some more gibberish
',
            'some gibberish
some more gibberish
',
            'some gibberish
some more gibberish
'
          ],
          [
            'some gibberish
some more gibberish
',
            'some gibberish
some more gibberish
',
            'some gibberish
some more gibberish
'
          ]
        ];
[download]

update: a little bug fixed, 'm' modifier added to second regexp, thanks to guha