public static function filter($str)
{
if (!MultiByte::valid_data($str)) {
return '';
} else {
do {
$_str = $str;
$str = self::strip_nulls($str);
$str = self::strip_illegal_entities($str);
$str = self::filter_html_elements($str);
} while ($str != $_str);
return $str;
}
}