What is titleProperty for nested element

Hello, I’m making my own nested element, I have refer to the Bricks’ accordtion-nested.php and slider-nested.php. There is one control I don’t understand its purpose and usecase which is 'titleProperty' => 'label' from:

public function set_controls() {
     $this->controls['sections'] = [
         'type'          => 'repeater',
         'titleProperty' => 'label',
         'items'         => 'children'

There is no definition as what it does and why we need it, can you please explain on this?