The object loaded is a SpatialPolygonsDataFrame object containing a slightly modified version of Bjoern Sandvik's improved version of world_borders.zip - TM_WORLD_BORDERS_SIMPL-0.2.zip dataset from the Mapping Hacks geodata site. The country Polygons objects and the data slot data frame row numbers have been set to the ISO 3166 three letter codes.
How to plot polygons with holes - holes are encoded by coordinates going anticlockwise, and overplotting is avoided by re-ordering the order in which polygons are plotted.