Many years ago, a hot-metal typesetter explained to me that kerning is done by using the area between letters as a guide rather than the separation between the bounding boxes. In the digital age this could potentially be automated. It's not a hard and fast rule and will require some small tweaks, but at a coarse approximation I think it shows promise.
this is just an illustration to accompany a discussion I'm having with -Rex- concerning letter spacing for pen text engines.
