4.2.1.6 LDP servers must publish any constraints on LDP clients’ ability to create or update LDPRs, by adding a Link header with an appropriate context URI, a link relation of http://www.w3.org/ns/ldp#constrainedBy, and a target URI identifying a set of constraints [RFC5988], to all responses to requests that fail due to violation of those constraints.

It must advertise that it imposes Annotation protocol specific constraints by including a link where the target IRI is http://www.w3.org/TR/annotation-protocol/, and the rel parameter value is the IRI http://www.w3.org/ns/ldp#constrainedBy.

Containers for related resources must support the same HTTP methods as described above for the Annotation Container, and must support identifying their type with a Link header. The constrainedBy link header on the response when dereferencing the Container should refer to a server specific set of constraints listing the types of content that are acceptable.

Inbox URLs can announce their own constraints (e.g., SHACL, Web Annotation Protocol) via an HTTP Link header or body of the resource with a rel value of http://www.w3.org/ns/ldp#constrainedBy.