my %allowed = ( u => 1, i => 1, b => 1);
my $text = "";
while ( my $token = $p->get_token ) {
    if($token->is_text) {
        $text .= $token->as_is;
    } elsif($token->is_tag && $allowed{$token->get_tag}) {
        $text .= $token->as_is;
    }
}