//TODO: the old version of this is working but this is slated to be rebuilt; will rewrite doc after that
A 9-patch is a rectangle drawn using a grid sprite.
The grid sprite is a 3x3 grid and with 9 blocks, representing the 4 corners, the 4 sides and the middle.
The corners are drawn at the same size, the sides are stretched on the side direction and the middle is expanded both ways.
Using this, you can get a box/rectangle that expands well to any sizes. This is useful for making panels, dialogs, borders.
See the nine_patch example app.