yii\validators\StringValidator::init PHP Method

    public function init()
    {
        parent::init();
        if (is_array($this->length)) {
            if (isset($this->length[0])) {
                $this->min = $this->length[0];
            }
            if (isset($this->length[1])) {
                $this->max = $this->length[1];
            }
            $this->length = null;
        }
        if ($this->encoding === null) {
            $this->encoding = Yii::$app->charset;
        }
        if ($this->message === null) {
            $this->message = Yii::t('yii', '{attribute} must be a string.');
        }
        if ($this->min !== null && $this->tooShort === null) {
            $this->tooShort = Yii::t('yii', '{attribute} should contain at least {min, number} {min, plural, one{character} other{characters}}.');
        }
        if ($this->max !== null && $this->tooLong === null) {
            $this->tooLong = Yii::t('yii', '{attribute} should contain at most {max, number} {max, plural, one{character} other{characters}}.');
        }
        if ($this->length !== null && $this->notEqual === null) {
            $this->notEqual = Yii::t('yii', '{attribute} should contain {length, number} {length, plural, one{character} other{characters}}.');
        }
    }

 public function init()
 {
     if ($this->message === null) {
         $this->message = \Yii::t('yii', '{attribute} must be a date.');
     }
     parent::init();
 }