iPhone5's 4inch screen has the problem when you tap the 'back' button on the navigation bar while you hold the device by one hand.
Apple insist there is no problems on them (in their ad), but in fact there is.
Recently, you can see the apps which has 'back' button on the tool bar (on the bottom of screen) or has function that swiping left to right in order to go back.
These are very functional, but seems temporary measures.
So we (@we6tr0n and @zuccoi) improved them and made the concept.
It is based on gesture and visual feedback, also it suits for the current iOS UI.