One of the features that Apple added to iOS 5 was the ability to split the iPad’s keyboard to the sides of the screen, making it much easier to type with both hands, as demonstrated in the picture above. Recently, it was discovered that Apple has included a subtle design tweak in the development of the keyboard to vastly improve the user experience.
This tweak comes in the form of six hidden buttons on either side of the keyboard, that mimic the letter buttons across the screen. This way, a small mistype, or forgetting that you are using the split keyboard won’t result in tapping empty space, but will rather type exactly the correct letter.
These subtle features are the kind of thing that make Apple products so easy to use. As iDB notes, this “hidden key” feature can also be seen in a hidden mic button when the international keyboard is enabled.