anchor.diff:  *** isInIterable: `true`
   *** index: `null`
   *** key: key
  +*** containerClass: `Map`
  +*** containerElementIndex: `0`
   ** When validating a constraint on the value type argument of `Map`, a node with the following properties will be added to the path:
   *** name: "<map value>"
   *** kind: `CONTAINER_ELEMENT`
   *** isInIterable: `true`
   *** index: `null`
   *** key: key
  +*** containerClass: `Map`
  +*** containerElementIndex: `1`
   * `java.util.Optional`
   ** No node will be appended to the path when validating type argument constraints on `Optional`
   * `javafx.beans.observable.ObservableValue`
  
positive.code: interface ContainerElementNode extends Node {
  
      /**
       * @return the type parameter affected by the violated constraint
       */
      TypeParameter getTypeParameter();
  }
  ----
  
  `getTypeParameter()` also needs to be added to `BeanNode` and `PropertyNode` and will return the affected type parameter when violating a class-level or property constraint in the course of cascaded validation of a generic type, such as `List` or `Map`.
  
  `TypeParameter` contains the information about the type parameter. It is designed as a simplified and serializable version of `java.lang.reflect.TypeVariable`:
  
  [source,java,indent=0]
  ----
  include::{validation-api-source-dir}javax/validation/TypeParameter.java[lines=7..8;12..-1]
  ----
  
  ==== Default extractors
  
  
negative.code: *** isInIterable: `false`
  *** index: the element's index
  *** key: `null`
  *** containerClass: `null`
  *** containerElementIndex: `null`
  * `java.util.Iterable` - excluding the case of `java.util.List` described below
  ** When `@Valid` is given on the iterable element itself, the element and all its entries will be validated; this is to grant backwards compatibility with BV 1.1
  ** When `@Valid` is given on the type parameter of an iterable element, all the entries will be validated.
  ** When validating a type argument constraint for `Iterable`, a node with the following properties will be added to the path:
  *** name: "<iterable element>"
  