We have taken a space-filling tiled approach in order to use screen space productively, avoiding the wasted background of the overlapped windows approach. Groups of windows stretch like an elastic material as they are being resized, and other windows shrink to make space. Figure 2 shows an example resizing of the HCIL window under the UMD group window in the former example pushing the surrounding windows to the sides proportional to their sizes.
Figure 2: Elastic resizing of the HCIL window in the space-filling tiled layout of elastic windows.
We have chosen the tiled window layout as our window organization style in order to maximize the visibility of windows for a task. People typically try to organize windows to be non-overlapping while working on a task, even when overlapping windows are allowed. Other windows are left beneath the working set of windows.
As Cohen et al.  stated, overlapping window layouts are difficult to handle when large numbers of windows must all be visible at once, and they come and go rapidly.
In tiled layouts, hierarchies of windows can be easily represented by the borders surrounding the subwindows. Users are quite flexible in the placement of subwindows in a group window. There is no strict horizontal or vertical placement rule. This feature allows some flexibility in the placement of windows under the same hierarchy and allows windows to conform to their content. The content of windows is an important constraint on which users determine the shape and size of windows.