0  +-----------------------------+
          | D-Space Header              |  ------+
          +-----------------------------+        |
          | D-Space Root                |        |
          | (includes overlay handler)  |        |
          +-----------------------------+        |
          | D-Space Segment 1           |        |
          +-----------------------------+        |
          | D-Space Segment 2           |        |
          +-----------------------------+        |
          | D-Space Segment n           |        |
          +-----------------------------+        |
          | I-Space Header              | <------+
          +-----------------------------+
          | I-Space Root                |
          | (includes overlay handler)  |
          +-----------------------------+
          | I-Space Segment 1           |
          +-----------------------------+
          | I-Space Segment 2           |
          +-----------------------------+
          | I-Space Segment n           |
          +-----------------------------+