--?   print(Screen_top1.line, Screen_top1.pos, Cursor1.line, Cursor1.pos, Screen_bottom1.line, Screen_bottom1.pos)

--?   print(Screen_top1.line, Screen_top1.pos, Cursor1.line, Cursor1.pos, Screen_bottom1.line, Screen_bottom1.pos)

  if byte_offset == nil then
    print(Cursor1.line, Cursor1.pos, byte_offset, Lines[Cursor1.line].data)
    assert(false)
  end