* elements of a given type. This is used to determine whether a 
     * pending element should be realized upon addition to this source.
     */
    void setSubscriptionVerifier(EventSubscriptionVerifier<T> typeSubscriptions);

    @Override
    void clear();

    boolean remove(Object o);

    @Override
    int size();

        return collection.removePendingCollection(providerOfT);
    }

    @Override
    public void onPendingAdded(Action<S> action) { }

    @Override
    public void setSubscriptionVerifier(EventSubscriptionVerifier<S> immediateRealizationSpec) {
        // The root element source is responsible for realizing elements of subscribed types.
    }

    @Override

        return removeByProvider(provider);
    }

    @Override
    public void onPendingAdded(Action<T> action) {
        this.addRealizedAction = action;
    }

    @Override
    public void setSubscriptionVerifier(EventSubscriptionVerifier<T> subscriptionVerifier) {
        this.subscriptionVerifier = subscriptionVerifier;
    }

    @Override
    public void realizeExternal(ProviderInternal<? extends T> provider) {