What does +9/7.2V mean?
7.2V at 1.2V per cell is a 6 cell battery.

9V at 1.5V per cell is a 6 cell battery.

It is most likely able to handle that range, so it can deal with NiCd/NiMH cell or standard Alkaline cells on battery powered instances. 

Edit: Looks like this is a duplicate of what supercat posted in the comments.  Sorry I missed that.