With the scroll() routine, the window is scrolled up one line. This involves moving the lines in the window data structure. As an optimization, if the scrolling region of the window
is the entire screen, the physical screen is scrolled at the same time.
With the scrl() and wscrl() routines, for positive n scroll the window up n lines (line i+n
becomes i); otherwise scroll the window down n lines. This involves moving the lines in the window character image structure. The current cursor position is
not changed.
For these functions to work, scrolling must be enabled via scrollok().
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