log(2, 'file navigator: '..chord)
  log(2, ('cursor initially at %d %s'):format(File_navigation.index, File_navigation.candidates[File_navigation.index]))

    end
  elseif chord == 'down' then
    file_navigator_down()
  elseif chord == 'up' then
    file_navigator_up()
  end
end
function file_navigator_up()
  local y, x, width = file_coord(File_navigation.index)
  local index = file_index(y-Editor_state.line_height, x, width)
  if index then
    File_navigation.index = index
  end
end
function file_navigator_down()
  local y, x, width = file_coord(File_navigation.index)
  local index = file_index(y+Editor_state.line_height, x, width)
  if index then
    File_navigation.index = index
  end
end
function file_coord(index)
  local y,x = Menu_status_bar_height, 5
  for i,filename in ipairs(File_navigation.candidates) do
    local width = App.width(to_text(filename))
    if x + width > App.screen.width - 5 then
      y = y + Editor_state.line_height
      x = 5
    end
    if i == index then
    return y, x, width
    end
    x = x + width + 30
  end
end
function file_index(fy, fx, fwidth)
  log_start('file index')
  log(2, ('for %d %d %d'):format(fy, fx, fwidth))
  local y,x = Menu_status_bar_height, 5
  local best_guess, best_guess_x, best_guess_width
  for i,filename in ipairs(File_navigation.candidates) do
    local width = App.width(to_text(filename))
    if x + width > App.screen.width - 5 then
      y = y + Editor_state.line_height
      x = 5

    if y == fy then
      log(2, ('%d: correct row; considering %d %s %d %d'):format(y, i, filename, x, width))
      if best_guess == nil then
        log(2, 'nil')
        best_guess = i
        best_guess_x = x
        best_guess_width = width
      elseif math.abs(fx + fwidth/2 - x - width/2) < math.abs(fx + fwidth/2 - best_guess_x - best_guess_width/2) then
        best_guess = i
        best_guess_x = x
        best_guess_width = width
      end
      log(2, ('best guess now %d %s %d %d'):format(best_guess, File_navigation.candidates[best_guess], best_guess_x, best_guess_width))
    end
    x = x + width + 30

  log_end('file index')
  return best_guess