The use of URIs taking the form of URLs in the http scheme (such as "http://www.w3.org/1999/xhtml") is common, despite the absence of any formal relationship with the HTTP protocol. The Namespaces specification does not say what should happen if such a URL is dereferenced (that is, if software attempts to retrieve a document from this location). One convention adopted by some users is to place an RDDL document at the location. In general, however, users should assume that the namespace URI is simply a name, not the address of a document on the Web.