This is essentially a List of AttributeMapping(s), but exposing an interface which is more suitable to our needs; in particular it expresses the immutable nature of this structure, and allows us to extend it with additional convenience methods such as indexedForEach(IndexedConsumer). And additional reason for the custom interface is to allow custom implementations which can be highly optimised as necessary for our specific needs; for example the implementation ImmutableAttributeMappingList is able to avoid caching problems related to JDK-8180450, which would not have been possible with a standard generic container.