The bounding box for the block. The vertices are in the order
of top-left, top-right, bottom-right, bottom-left. When a
rotation of the bounding box is detected the rotation is
represented as around the top-left corner as defined when the
text is read in the 'natural' orientation. For example: -
when the text is horizontal it might look like: ::
0----1 | | 3----2 - when it's rotated 180
degrees around the top-left corner it becomes: ::
2----3 | | 1----0 and the vertice order will
still be (0, 1, 2, 3).
Detected block type (text, image etc) for this block.
