What does this [$var] operator do?

Question

Yii

This code generates Gii

public function forCategory($id)
    {
        $ids = [$id];
        $childrenIds = [$id];
        ...
    }

I don't fully understand what's going on here :)

Answer 1

Creates an array with one element $var.

Answer 2

The "new" way to define an array as of PHP 5.4