A Microsoft file hosting and synchronization service.
What notification do you get when you try to make a copy of a file and place it in the same folder?
Currently, I'm using 3rd-party software to confirm what I'm trying to do. If two files have the same name, the software asks me if I would like to replace the existing file. If I say NO and select "keep both copies", the software appends a number to the name.
So, I no longer know what the default Windows behavior is when creating duplicates.