A stacking window manager (also called floating window manager) is a window manager that draws all windows in a specific order, allowing them to overlap, using a technique called painter's algorithm. All window managers that allow the overlapping of windows but are not compositing window managers are considered stacking window managers, although it is possible that not all use exactly the same methods. Other window managers that are not considered stacking window managers are those that do not allow the overlapping of windows. These are called tiling window managers. Stacking window managers allow windows to overlap by drawing them one at a time. Stacking, or repainting (in reference to painter's algorithm) refers to the rendering of each window as an image, painted directly over the desktop, and over any other windows that might already have been drawn, effectively erasing the areas that are covered. The process usually starts with the desktop, and proceeds by drawing each window and any child windows from back to front, until finally the foreground window is drawn. The order in which windows are to be stacked is called their z-order.