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Note: The following is an excerpt from the official IETF RFC. It is provided here as a convenience and is not authoritative. Refer to the original document as the authoritative reference.

The Uniform Resource Identifier (URI) protocol element and generic syntax is defined by [RFC3986]. Each URI begins with a scheme name, as defined by Section 3.1 of RFC 3986, that refers to a specification for identifiers within that scheme. The URI syntax provides a federated and extensible naming system, where each scheme's specification can further restrict the syntax and define the semantics of identifiers using that scheme.

This document obsoletes [RFC4395], which in turn obsoleted [RFC2717] and [RFC2718]. Recent documents have used the term “URI” for all resource identifiers, avoiding the term “URL” and reserving the term “URN” explicitly for those URIs using the “urn” scheme name [RFC2141]. URN “namespaces” [RFC3406] are specific to the “urn” scheme and are not covered explicitly by this specification.

This document provides updated guidelines for the definition of new schemes, for consideration by those who are defining, registering, or evaluating those definitions. In addition, this document provides an updated process and mechanism for registering schemes within the IANA URI Schemes registry. There is a single namespace for registered schemes. The intent of the registry is to:

• provide a central point of discovery for established URI scheme names and easy location of defining documents for schemes;
• discourage multiple separate uses of the same scheme name;
• help those proposing new scheme names to discern established trends and conventions and to avoid names that might be confused with existing ones; and
• encourage registration by setting a low barrier for registration.