code: private List<ClassDocImpl> getClasses(boolean filtered) {
          if (allClasses != null && !filtered) {
              return allClasses;
          }
          if (allClassesFiltered != null && filtered) {
              return allClassesFiltered;
          }
          ListBuffer<ClassDocImpl> classes = new ListBuffer<>();
          for (Symbol enumerated : sym.members().getSymbols(NON_RECURSIVE)) {
              if (enumerated != null) {
                  ClassSymbol s = (ClassSymbol)enumerated;
                  ClassDocImpl c = env.getClassDoc(s);
                  if (c != null && !c.isSynthetic())
                      c.addAllClasses(classes, filtered);
              }
          }
          if (filtered)
              return allClassesFiltered = classes.toList();
          else
              return allClasses = classes.toList();
      }
docs: Return a list of all classes contained in this package, including
  member classes of those classes, and their member classes, etc.