which had no Root Element. This likely means the XML is malformed or missing

今天按照古月老师的步骤，想在RViz中配置插件。

按步骤做下来后，一运行，出现如下错误：

[E[ERROR] [1523370744.057263390]: Skipping XML Document "/home/zhan/catkin_ws/src/rviz_telop_commander/plugin_description.xml" which had no Root Element.  This likely means the XML is malformed or missing.
在网上查找了几个答案。都是这样或者这样的。古月老师是用的《Mastering ROS for Robotics Programming》这本书的第六章实例，遂查原书原码，发现问题是plugin_description.xml的位置放错了！！！

解决方案：xml文件和xml文件放在一起就好了。