A screen window is a rectangular region on the terminal screen
    through which you can view a display. The SET WINDOW command
    establishes a window definition by associating a window name
    with a screen region. You specify the screen region in terms of a
    starting line and height (line count) and, optionally, a starting
    column and width (column count). If you do not specify the
    starting column and column count, the starting column defaults
    to column 1 and the column count defaults to the current screen
    width.

    You can specify a window region in terms of expressions that use
    the built-in symbols %PAGE and %WIDTH.

    You can use the names of any windows you have defined with the
    SET WINDOW command in a DISPLAY command to position displays on
    the screen.

    Window definitions are dynamic-that is, window dimensions expand
    and contract proportionally when a SET TERMINAL command changes
    the screen width or height.

    Related commands:

       DISPLAY
       (SHOW,CANCEL) DISPLAY
       (SET,SHOW) TERMINAL
       (SHOW,CANCEL) WINDOW