<input type="text" id="keywords" name="keywords" class="text" size="20" />
nature, index, luxury, test1, test2, ..... test60
if (isset($_POST['submit'])){
$kw = $_POST['keywords'];
$kw = preg_replace("/\s+/", " ", $kw);
$kwArr = explode(' ', $kw);
$output = array_slice($kwArr, 5, count($kwArr));
$output = array_diff($kwArr, $output);
for($i = 0; $i<count($output); $i++){
if (strlen($output[$i]) <= 20){
$result[] = $output[$i];
}
}
$keywords = implode(', ', $result);
echo $keywords;
}
Cheers