The Node has the following code which allows user to add an arbitrary name-value pair to Node. It proved to be very useful. I hope the ObjectProperty could have this method so that we can add name-value pair to an ObjectProperty. Personally I don't care if the properties will be included in persistence, toString, hashCode, equal.

    // A map containing a set of properties for this node
    private ObservableMap<Object, Object> properties;

    /**
      * Returns an observable map of properties on this node for use primarily
      * by application developers.
      *
      * @return an observable map of properties on this node for use primarily
      * by application developers
      */
     public final ObservableMap<Object, Object> getProperties() {
        if (properties == null) {
            properties = FXCollections.observableMap(new HashMap<Object, Object>());
        }
        return properties;
    }