code: public static Set<Integer> getApplicableHistoryTypes() {
  		Set<Integer> allApplicableTypes = new HashSet<Integer>();
  		allApplicableTypes.addAll(PluginPassiveScanner.getDefaultHistoryTypes());
  		if (!optedInHistoryTypes.isEmpty()) {
  			allApplicableTypes.addAll(optedInHistoryTypes);
  		}
  		return allApplicableTypes;
  	}
docs: Returns the full set (both default and "opted-in") which are to be
  applicable for passive scanning.
  
  @return a set of {@code Integer} representing all of the History Types
  which are applicable for passive scanning.
  @since TODO add version