code: public void update(
  			long id, GpsTraceDetails.Visibility visibility, String description, List<String> tags)
  	{
  		checkFieldLength("Description", description);
  		checkTagsLength(tags);
  		
  		GpsTraceWriter writer = new GpsTraceWriter(id, visibility, description, tags);
  		
  		osm.makeAuthenticatedRequest(GPX + "/" + id, "PUT", writer);
  	}
docs: Change the visibility, description and tags of a GPS trace. description and tags may be null
  if there should be none.
  
  @throws OsmNotFoundException if the trace with the given id does not exist
  @throws OsmAuthorizationException if this application is not authorized to write traces
  (Permission.WRITE_GPS_TRACES)
  OR if the trace in question is not the user's own trace
  @throws IllegalArgumentException if the length of the description or any one single tag
  is more than 256 characters