The display of images is Sequence Generator Pro is handled through "Image Containers". An "Image Container" is really just a window that can be docked (tabbed), nested in other windows or popped out to float above other windows.
The idea is to provide a highly flexible and useful environment in which to display and view images. For example, you can keep all of your windows tabbed or you can display two images side by side for comparison.
We call these windows "Image Containers" because they retain their own set of properties (like stretching values, inversion crosshairs, etc). If a new image is swapped out in the same container it will inherit all of the container's properties.