I wrote some JavaSE sample to test the new ValueExtractor classes for JavaFX like ListPropertyValueExtractor. In that case I miss an important feature in the base API.

Let's say I have a model that has the following fields:

    @NotEmpty(message = "Name sollte nicht leer sein!")
    private final StringProperty name = new SimpleStringProperty();

    private final Property<@Min(50) Integer> count = new SimpleObjectProperty<>();

    @Size(min=1, max=4)
    private final ListProperty<@Size(min=2, max=32) String> tags = new SimpleListProperty<>(FXCollections.observableArrayList());

Next I bind all the properties of the model to UI nodes. Example:

 nameField.textProperty().bindBidirectional(model.nameProperty());

In addition I want to do a validation call whenever a value in the model changes. For the name property this can be done by the following code:

nameErrorNode.visibleProperty().bind(Bindings.createBooleanBinding(() ->
                        !validator.validateProperty(model, "name").isEmpty(),
                model.nameProperty()));

By doing it like this only the name property will be validated whenever it changes. It would be wrong to validate the complete model in this case.
I can simply do the same for the list:

tagErrorNode.visibleProperty().bind(Bindings.createBooleanBinding(() ->
                        !validator.validateProperty(model, "tags").isEmpty(),
                model.tagsProperty()));

In this case the list will be validated whenever the list changes. This happens for example if a new element will be added, updated or removed. Let's imagine a list with 1_000_000 entries or so. In that case I do not want to validate the complete list when I update an element. Based on this I think that an additional method next to

Validator.validateProperty()

is needed in the JBV Spec to validate internal elements.