Memory Layout (Bytefield)

(draw-column-headers)
(draw-box "Address" {:span 4})
(draw-box "Size" {:span 2})
(draw-box 0 {:span 2})
(draw-gap "Variable-length data")
(draw-box nil :box-below)
(draw-box "Next Address" {:span 4})
(draw-box "Block Size" {:span 2})
(draw-gap "Optional extension" {:min-label-columns 6})
(draw-bottom)