anchor.diff:          {value, Page} -> Page;
           false -> undefined
       end.
  +
  
positive.code:     keepalive/1, 
      keepalive/2, 
      ensure_page_session/1,
      add_script/2,
      add_script/1,
      check_expire/2,
  
negative.code:     Context2 = Context1#context{page_id=NewPageId, page_pid=NewPage#page.page_pid},
      {reply, Context2, Session1};
  
  handle_call(get_attach_state, _From, Session) ->
      {reply, [z_session_page:get_attach_state(Pid) ||  #page{page_pid=Pid} <- Session#session.pages], Session};
  
  handle_call(Msg, _From, Session) ->
      {stop, {unknown_cast, Msg}, Session}.
  
  