This module provides an implementation of OpenURLs encoded as URIs
(Key/Encoded-Value (KEV) Format), this forms only a part of the OpenURL
spec. It does not check that OpenURLs constructed are sane according to
the OpenURL specification (to a large extent sanity will depend on the
community of use).

From the implementation guidelines:

The description of a referenced resource, and the descriptions of the
associated resources that comprise the context of the reference, bundled
together are called a ContextObject. It is a ContextObject that is
transported when a user makes a request by clicking a link. A KEV OpenURL
may contain only one ContextObject.

The ContextObject may contain up to six Entities. One of these, the
Referent, conveys information about the referenced item. It must always be
included in a ContextObject. The other five entities - ReferringEntity,
Requester, Resolver, ServiceType and Referrer - hold information about the
context of the reference and are optional.

WWW: https://metacpan.org/release/URI-OpenURL