yii\base\Model::offsetSet PHP Метод

This method is required by the SPL interface [[\ArrayAccess]]. It is implicitly called when you use something like $model[$offset] = $item;.

public offsetSet ( integer $offset, mixed $item )
$offset	integer	the offset to set element
$item	mixed	the element value

    public function offsetSet($offset, $item)
    {
        $this->{$offset} = $item;
    }

Model