18.104.22.168 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. For example, a server that refuses resource creation requests via HTTP PUT, POST, or PATCH would return this Link header on its 4xx responses to such requests. The same Link header may be provided on other responses. LDP neither defines nor constrains the representation of the link's target resource. Natural language constraint documents are therefore permitted, although machine-readable ones facilitate better client interactions. The appropriate context URI can vary based on the request's semantics and method; unless the response is otherwise constrained, the default (the effective request URI) should be used.