anchor.diff:  *** index: the element's index
   *** key: `null`
   *** containerClass: `List`
  -*** containerElementIndex: `0`
  +*** typeArgumentIndex: `0`
   * `java.util.Map`
   ** When `@Valid` is given on the map element itself, the element and all its values will be validated; this is to grant backwards compatibility with BV 1.1
   ** When `@Valid` is given on the key type parameter, the map keys will be validated
  
positive.code: interface ContainerElementNode extends Node {
  
      /**
       * @return the class of the container for the element affected by the violated constraint
       */
      Class<?> getContainerClass();
  
      /**
       * @return the index of the type parameter affected by the violated constraint in the container class
       */
      Integer getContainerElementIndex();
  }
  ----
  
  `getContainerClass()` and `getContainerElementIndex()` also need 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`.
  
  ==== Default extractors
  
  
negative.code: *** index: the element's index if the iterable is of type `List` or a subtype thereof; `null` otherwise
  *** key: `null`
  *** containerClass: `Iterable`
  *** typeArgumentIndex: `0`
  * `java.util.List`
  ** 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.
  