The default read-only implementation of Reference.
The default read-only implementation of Reference. You typically should not need to directly reference this class; instead, use the Reference.apply method to construct new instances.
This Proxy trait allows you to extend the Reference trait with additional state or behavior and implement the read-only methods from Reference using an underlying instance.
Field information in declaration order.
Checks that all required fields are non-null.
An external reference applied to content
An external reference typically refers to a thing in another system or a real world thing. Examples include the isbn of a book the content is reviewing or a cricket match.