yii\behaviors\SluggableBehavior::isNewSlugNeeded PHP Method

    protected function isNewSlugNeeded()
    {
        if (empty($this->owner->{$this->slugAttribute})) {
            return true;
        }
        if ($this->immutable) {
            return false;
        }
        foreach ((array) $this->attribute as $attribute) {
            if ($this->owner->isAttributeChanged($attribute)) {
                return true;
            }
        }
        return false;
    }