First slide
Test line

Second line
Line with explicit font size @20


##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;
use Parse::RecDescent;
use Data::Dumper;

$::RD_ERRORS = 1;
$::RD_WARN   = 1;
$::RD_HINT   = 1;
$::RD_TRACE  = 1;

my $grammar = <<'END_GRAMMAR';
#<autotree>

startrule: slide(s)

slide: <skip: qr/[ \t]*/> line(s) line_end(s)

line: text fontspec(?) line_end 

text: /[^@\n]+(?:\b@[^@\n]*)*/

fontspec: <skip: ''> "@" fontspec_size

fontspec_size: /\d+/
             | <error: Invalid fontspec or unescaped '\@' at:\n$text.>

line_end: "\n"

END_GRAMMAR

my $good_text = <<'SAMPLE_TEXT';
Test
Line @20

Even more test address@test.com @20
Escaped \@text

SAMPLE_TEXT

my $bad_text =  <<'SAMPLE_TEXT';

Bad line @invalid
Also bad @foo @20

SAMPLE_TEXT

my $parser = new Parse::RecDescent ($grammar);
#$parser->startrule($text);

$parser->startrule($good_text);
print STDERR "\n" x 3;
$parser->startrule($bad_text);