Library path argument in plugin.xml

Hi, In the tutorials, it says that the [plugin.xml should start with](http://wiki.ros.org/rqt/Tutorials/Create%20your%20new%20rqt%20plugin#Create_plugin.xml_file): Which implies that in `my_pkg/src/my_pkg` there is a plugin. However, in [some other codes](https://github.com/ros-visualization/rqt_robot_plugins/blob/master/rqt_rviz/plugin.xml) out there I see something like Which one is supposed to be correct? In fact, sometimes `src` is enough but some other times I have to write `src/my_pkg` or it will not be able to load the plugin. Some further explanation on this would be great. Thanks!