docs: public final ExtensionComponentSet filtered() {
          final ExtensionComponentSet base = this;
          return new ExtensionComponentSet() {
              @Override
              public <T> Collection<ExtensionComponent<T>> find(Class<T> type) {
                  List<ExtensionComponent<T>> a = Lists.newArrayList();
                  for (ExtensionComponent<T> c : base.find(type)) {
                      if (ExtensionFilter.isAllowed(type,c))
                          a.add(c);
                  }
                  return a;
              }
          };
      }