function App.mousefocus(in_focus)
  if current_app_is_warning() then return end
  if Current_app == 'run' then
    if run.mouse_focus then run.mouse_focus(in_focus) end
  elseif Current_app == 'source' then
    if source.mouse_focus then source.mouse_focus(in_focus) end
  else
    assert(false, 'unknown app "'..Current_app..'"')
  end
end