-- cursor on final screen line (A or B side) => goes to next screen line on A side
-- cursor on B side => move down one screen line (B side) in current line
-- cursor on A side => move down one screen line (A side) in current line

    end
  elseif State.cursor1.posB then
    -- move down one screen line (B side) in current line
    local scroll_down = false
    if Text.le1(State.screen_bottom1, State.cursor1) then
      scroll_down = true
    end
    local cursor_line = State.lines[State.cursor1.line]
    local cursor_line_cache = State.line_cache[State.cursor1.line]
    local cursor2 = Text.to2(State, State.cursor1)
    assert(cursor2.screen_lineB < #cursor_line_cache.screen_line_starting_posB)
    local screen_line_starting_posB, screen_line_indexB = Text.pos_at_start_of_cursor_screen_lineB(State)
    new_screen_line_starting_posB = cursor_line_cache.screen_line_starting_posB[screen_line_indexB+1]
    local new_screen_line_starting_byte_offsetB = Text.offset(cursor_line.dataB, new_screen_line_starting_posB)
    local s = string.sub(cursor_line.dataB, new_screen_line_starting_byte_offsetB)
    State.cursor1.posB = new_screen_line_starting_posB + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
    if scroll_down then
      Text.snap_cursor_to_bottom_of_screen(State)

    -- move down one screen line in current line

    -- move down one screen line (A side) in current line

  for i=#State.line_cache[State.cursor1.line].screen_line_starting_pos,1,-1 do
    local spos = State.line_cache[State.cursor1.line].screen_line_starting_pos[i]

  local cursor_line_cache = State.line_cache[State.cursor1.line]
  for i=#cursor_line_cache.screen_line_starting_pos,1,-1 do
    local spos = cursor_line_cache.screen_line_starting_pos[i]

    end
  end
  assert(false)
end
function Text.pos_at_start_of_cursor_screen_lineB(State)
  Text.populate_screen_line_starting_posB(State, State.cursor1.line)
  local cursor_line_cache = State.line_cache[State.cursor1.line]
  for i=#cursor_line_cache.screen_line_starting_posB,1,-1 do
    local sposB = cursor_line_cache.screen_line_starting_posB[i]
    if sposB <= State.cursor1.posB then
      return sposB,i

  local line = State.lines[State.cursor1.line]

  return screen_lines[#screen_lines] <= State.cursor1.pos

  if (not State.expanded and not line.expanded) or
      (line.dataB == nil or #line.dataB == 0) then
    return screen_lines[#screen_lines] <= State.cursor1.pos
  end
  if State.cursor1.pos then
    -- ignore B side
    return screen_lines[#screen_lines] <= State.cursor1.pos
  end
  assert(State.cursor1.posB)
  local line_cache = State.line_cache[State.cursor1.line]
  local x = Margin_left + Text.screen_line_width(State, State.cursor1.line, #line_cache.screen_line_starting_pos) + AB_padding
  Text.populate_screen_line_starting_posB(State, State.cursor1.line, x)
  local screen_lines = State.line_cache[State.cursor1.line].screen_line_starting_posB
  return screen_lines[#screen_lines] <= State.cursor1.posB