$conf = array(
  'username' => array('isEmpty', 'isUnique' => array('ident' => 'name', 'sanitize' => 'username')),
  'pass' => array('range' => array('min' => 6, 'max' => 20))
);

$validator = new Validator;
$validator->setConfig($conf);
if (!$validator->isValid()) $errors = $validator->getErrors();