Some URIs refer to specific variants of an object, and some refer to objects with many variants. In the latter case, the representations, encodings, and languages acceptable may be specified in the header request fields, and may affect the particular value which is returned.
Other possible replies allow a set of URIs to be returned to the client, who may use them to retrieve the object. This allows name servers to be implemented using HTTP, and also forwarding address to be given when objects have been moved.