src/Knp/Menu/Factory/CoreExtension.php
private function buildExtras(ItemInterface $item, array $options)
    {
        if (!empty($options['extras'])) {
            foreach ($options['extras'] as $key => $value) {
                $item->setExtra($key, $value);
            }
        }
    }
private function buildExtras(ItemInterface $item, array $options)
    {
        if (!empty($options['extras'])) {
            foreach ($options['extras'] as $key => $value) {
                $item->setExtra($key, $value);
            }
        }
    }
Configures the newly created item's extras
Extras are processed one by one in order not to reset values set by other extensions

@param ItemInterface $item
@param array         $options