a 标签触发器 href="" 时，为什么点击后弹出当前页面？
<div class="panel-group" id="accordion"> <div class="panel panel-default"> <div class="panel-heading"> <h4 class="panel-title"><a href="" data-toggle="collapse" data-target="#aa1">标题一</a></h4> </div> <div class="panel-collapse collapse in" id="aa1"> <div class="panel-body">标题一对应的内容</div> </div> </div> </div>
