How does POST to an LDPC that supports multiple creationTypes indicate which resource to create?

An OPTIONS request on an LDPC could return multiple Link: headers with rel="http://open-services.net/ns/core#creationType" indicating the container can support multiple resource types. The Accept-Post header indicates the entity request body format, but does not specify the resource type expressed by that content. RDF resources could specify their type directly in an assertion, but this is not available for LDP-NR (Non-RDF) sources.

Section A.1.2 creationType seems to indicate that this could be used on a Link-relation rel value for POST, but this should be explicitly specified and have an example.

A related issue is that an HTTP OPTIONS request on an LDPC can also return multiple Link: headers with rel="http://www.w3.org/ns/ldp#constrainedBy". A POST or PUT to create or update a resource can use return this header when the request fails because of violation of the constraint. But there is currently no way to associate multiple creationType and constrainedBy link relations for an LDPC. The constraindBy link may need to include a context IRI (anchor parameter) to identify the resource type that is being constrained.