A new scheme may be introduced by defining a mapping onto a conforming URL syntax, using a new prefix. URLs for experimental schemes may be used by mutual agreement between parties. Scheme names starting with the characters "x-" are reserved for experimental purposes.
The Internet Assigned Numbers Authority (IANA) will maintain a registry of URL schemes. Any submission of a new URL scheme must include a definition of an algorithm for accessing of resources within that scheme and the syntax for representing such a scheme.
URL schemes must have demonstrable utility and operability. One way to provide such a demonstration is via a gateway which provides objects in the new scheme for clients using an existing protocol. If the new scheme does not locate resources that are data objects, the properties of names in the new space must be clearly defined.
New schemes should try to follow the same syntactic conventions of existing schemes, where appropriate. It is likewise recommended that, where a protocol allows for retrieval by URL, that the client software have provision for being configured to use specific gateway locators for indirect access through new naming schemes.
The following scheme have been proposed at various times, but this document does not define their syntax or use at this time. It is suggested that IANA reserve their scheme names for future definition:
afs Andrew File System global file names. mid Message identifiers for electronic mail. cid Content identifiers for MIME body parts. nfs Network File System (NFS) file names. tn3270 Interactive 3270 emulation sessions. mailserver Access to data available from mail servers. z39.50 Access to ANSI Z39.50 services.