Custom KeywordValidator - SilverStripe

<?php
class KeywordValidator extends Validator {
    public function php($data) {
        $keywords = preg_replace('/^[^_A-z- ]+$/', '', $data['Keywords']);
        $tags = explode(' ', $keywords);
        $fail = false;
        if (count($tags) < 3) {
            $fail = true;
        }
        if (!$fail) {
            foreach ($tags as $tag) {
                if (strlen($tag) === 0) {
                    $fail = true;
                }
            }
        }
        if ($fail) {
            $this->validationError('Keywords', 'There must be at least 3 valid keywords');
            return false;
        }
        return true;
    }

    public function javascript() {
        //echo "alert('somethingspecial');";
        return false;
    }
}

class MyPage extends Page {
    public function getCMSValidator() {
        $validator = new KeywordValidator();
        return $validator;
    }
}