Nine-patch images allow optional definition of the padding lines in the image. The padding lines are the lines on the right and at the bottom.
If a View sets the 9-patch image as its background, the padding lines are used to define the space for the View's content (e.g. the text input in an
EditText). If the padding lines are not defined, the left and top lines are used instead.
The content area of the stretched image then looks like this: