CDateValidator

protected function validateAttribute($object,$attribute)
{
    $value=$object->$attribute;
    if($this->allowEmpty && $this->isEmpty($value))
        return;

    $valid=false;

    // reason of array checking is explained here: https://github.com/yiisoft/yii/issues/1955
    if(!is_array($value))
    {
        $formats=is_string($this->format) ? array($this->format) : $this->format;
        foreach($formats as $format)
        {
            $timestamp=CDateTimeParser::parse($value,$format,array('month'=>1,'day'=>1,'hour'=>0,'minute'=>0,'second'=>0));
            if($timestamp!==false)
            {
                $valid=true;
                if($this->timestampAttribute!==null)
                    $object->{$this->timestampAttribute}=$timestamp;
                break;
            }
        }
    }

    if(!$valid)
    {
        $message=$this->message!==null?$this->message : Yii::t('yii','The format of {attribute} is invalid.');
        $this->addError($object,$attribute,$message);
    }
}