code: public Set<Integer> getZoomLevels() {
  		final Set<Integer> zoomLevels = new TreeSet<Integer>();
  
  		for (final GEMFRange rs: mRangeData) {
  			zoomLevels.add(rs.zoom);
  		}
  
  		return zoomLevels;
  	}
docs: /*
  Return list of zoom levels contained within this archive.