public static function isSeparator($str)
{
// NOTES: Only non alphanumeric ASCII characters may be separators.
// `~` is the last printable ASCII character.
return $str <= '~' && $str !== '_' && ($str < '0' || $str > '9') && ($str < 'a' || $str > 'z') && ($str < 'A' || $str > 'Z');
}