public function testDigets()
{
$string = " 0 1 a2b 3c!@#\$%^&*()-= <>\t";
isSame('0123', Filter::_($string, 'digits'));
isSame('abc', Filter::_($string, 'alpha'));
isSame('01a2b3c', Filter::_($string, 'alphanum'));
}