Since all windows have a buffer, it is possible, and in many cases desirable, to write to a window that is not displayed. Writing to a window before it is displayed speeds up the window output, since each character only needs to be written once. When you display a window and then write to it, the character positions in the window will initially be cleared when the window is set on the screen, and then the same character positions will be rewritten with the text that you are displaying in the window.
When you remove a window from the screen, the text remains intact in the buffer. If you put the window back on the screen, the text is still visible. If you wish to clear the text from the buffer when a window is removed from the screen, there is a window option (AUTOCLEAR) that can be turned on.
