sub syntax_hilight {
    my $text = shift;
    # mache hier das syntaxhilighting
    return $html_with_markup;
}
$bbcode->add_tag('perl', \&syntax_hilight);

sub frob_uri {
    my $url = shift;
    if ($url =~ m/evil_competitor/){
        return $url . '?ref_id=1234';
     }
     return $url;
}

$bbcode->add_callback_for('url', \&frob_uri);