In Elastic Windows, an empty window can be created as a ``container'' window by double-clicking on an existing window border. The location of the new window depends on the location of that border as in the open operation. Container windows are typically created for the purpose of grouping related pieces of information and applying window operations on all of them at once. Once a window group is created, dragging and dropping objects inside this window puts the windows for each object into the group (Figure ). A separate window is opened for each object as a member of the group, surrounded by the container window borders. Objects can also be added and removed from the group at any time. Users can also open container windows within container windows to build a hierarchy of windows suitable for their task. When operations are applied on the group window, its effects are propagated to all lower-level windows in the group recursively.