根据
the bootstrap document，添加aria-hidden =“true”表示辅助技术跳过模态的DOM元素，这解释了主模态div中存在aria-hidden = true。
在模态标题div中为模态关闭按钮添加aria-hidden = true的目的是什么？
@H_502_4@<!-- Modal --> <div class="modal fade" id="myModal" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true"> <div class="modal-dialog"> <div class="modal-content"> **<*div class="modal-header"> <button type="button" class="close" data-dismiss="modal" aria-hidden="true">× </button> <h4 class="modal-title" id="myModalLabel">Modal title</h4> </div>*** <div class="modal-body"> ... </div> <div class="modal-footer"> <button type="button" class="btn btn-default" data-dismiss="modal">Close</button> <button type="button" class="btn btn-primary">Save changes</button> </div> </div><!-- /.modal-content --> </div><!-- /.modal-dialog --> </div><!-- /.modal -->