code: public void
  setCache(Cache cache) {
  	if (cache == null) {
  		this.cache = new Cache(dclass);
  		this.temporary_cache = true;
  	} else {
  		this.cache = cache;
  		this.temporary_cache = false;
  	}
  }
docs: Sets the cache to use when performing this lookup.  This overrides the
  default value.  If the results of this lookup should not be permanently
  cached, null can be provided here.
  @param cache The cache to use.