A plugin is a dynamically loaded chunk of code. It can exist as a child of world, model, and sensor. A unique name for the plugin, scoped to its parent. Name of the shared library to load. If the filename is not a full path name, the file will be searched for in the configuration paths. This is a special element that should not be specified in an SDF file. It automatically copies child elements into the SDF element so that a plugin can access the data.