What is #[] construct in PHP / Yii2?

I’ve been long, long time away from Yii 2. When I’ve come back, I have noticed a #[] construct for arrays, used by Yii 2, coming most likely from PHP 8:

#[AtLeast(['email', 'phone'])]
#[Length(min: 2)]

I did some Internet search for this:

But found nothing.

Can anyone shed some light here or point me to the right piece of documentation. Thank you.

This is Yii 3.

You are looking at new attributes syntax.

Thank you for your explanation.