Rectangle
From GNUpdf
Rectangles are used to describe locations and bounding boxes.
A rectangle is specified using an array composed by four numbers: the coordinates of of two diagonally opposited corners of the rectangle.
For example:
[ll_x ll_y ur_x ur_y]
Note that it is permitted to specify any two diagonally opposite corners. That implies we should normalize it.
The GNU PDF library normalizes rectangles into the lower left and upper right corners.
