--?       print('previous screen line starts at pos '..tostring(screen_line_starting_pos)..' of its line')
      if State.screen_top1.line > State.cursor1.line then
        State.screen_top1.line = State.cursor1.line
        State.screen_top1.pos = screen_line_starting_pos
--?         print('pos of top of screen is also '..tostring(State.screen_top1.pos)..' of the same line')
      end

    local new_screen_line_starting_byte_offset = Text.offset(State.lines[State.cursor1.line].data, new_screen_line_starting_pos)
    local s = string.sub(State.lines[State.cursor1.line].data, new_screen_line_starting_byte_offset)

  local botpos = Text.pos_at_start_of_cursor_screen_line(State)