What happens when you press SHIFT and ALT and drag a rectangular marquee over an area?

When you press SHIFT and ALT while dragging a rectangular marquee, the tool behaves in a specific way to create a selection. The SHIFT key typically constrains the shape to a perfect square, while the ALT key allows the selection to be made from the center outwards rather than from one corner. This means that the selection will maintain equal dimensions on both sides of the starting point, creating a square that expands outwards from the center of where you initially clicked.

This combination of key presses is valuable in design work as it enables precise and symmetrical selections, which can be essential when cropping or editing images. The perfect square selection ensures that your selected area is proportionate, making it easier to maintain visual balance in your design tasks.