Paul Tangrini - 2009-03-17

I would like to create displays of the form

Block_1   Block_2   Block_3
Block_4   Block_5   Block_6

where 1) the Blocks 1,2,4,5 have aligned rows and columns
          2) Blocks 3 and 4 should display text that spans
              the full width of the corresponding Blocks 1,2 and 4,5
              to their left

Q: How could on build this?
There does not appear to be a concept of spanning
rows and columns  for Tikz matrices.

Note that the vertical length of Block_3 might exceed the
vertical length of Block_1,2

Q: Is there a way of adding matrix style left and right braces
    around each of the blocks?