There is a small bug that has been introduced into Adobe illustrator a few versions ago that hasn't been corrected. I simply want to make you aware of it so that the development team can take a look. When creating a new file and entering in the dimensions, the dimension values can't be 'selected and deleted'. They don't highlight so you can't select and delete them like you can any other value box in illustrator. You have to click into them, then hit the backspace. It's minor but annoying that they don't work the same way as everything else.