The bar is called the system track. The check-box on the right makes a system selection (it includes all objects including hidden system objects). The bin on the left deletes everything, including hidden system objects.
Hi Daniel,
Thank you very much for you swift and very accurate answer… you saved my day.
I was also a bit puzzled since I use the French version of the software, and it can sometimes be cumbersome to find how to apply the tips you find in the English tutorials and forums to a different language version.