5.1 防止页面显示在框架中

• 防止页面被拦截，添加 JavaScript 代码，而嵌入新的页面；(实际不太明白)

• back 按钮有效

    <script>
        if (top.location != self.location) {
            top.location.replace(self.location);
        }
    </script>

• back 按钮无效

    <script>
        if (top.location != self.location) {
            top.location = self.location;
        }
    </script>