Guidelines and Registration Procedures for URI Schemes
draft-ietf-appsawg-uri-scheme-reg-05

Network Working Group                                     D. Thaler, Ed.
Internet-Draft                                                 Microsoft
Obsoletes: 4395 (if approved)                                  T. Hansen
Intended status: Best Current Practice                 AT&T Laboratories
Expires: September 28, 2015                                    T. Hardie
                                                                  Google
                                                             L. Masinter
                                                                   Adobe
                                                          March 27, 2015

         Guidelines and Registration Procedures for URI Schemes
                  draft-ietf-appsawg-uri-scheme-reg-05

Abstract

   This document updates the guidelines and recommendations, as well as
   the IANA registration processes, for the definition of Uniform
   Resource Identifier (URI) schemes.  It obsoletes RFC 4395.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 28, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  URIs and IRIs . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Requirements for Permanent Scheme Definitions . . . . . . . .   4
     3.1.  Demonstrable, New, Long-Lived Utility . . . . . . . . . .   4
     3.2.  Syntactic Compatibility . . . . . . . . . . . . . . . . .   5
     3.3.  Well-Defined  . . . . . . . . . . . . . . . . . . . . . .   5
     3.4.  Definition of Operations  . . . . . . . . . . . . . . . .   6
     3.5.  Context of Use  . . . . . . . . . . . . . . . . . . . . .   7
     3.6.  Internationalization and Character Encoding . . . . . . .   7
     3.7.  Clear Security Considerations . . . . . . . . . . . . . .   7
     3.8.  Scheme Name Considerations  . . . . . . . . . . . . . . .   8
     3.9.  Interoperability Considerations . . . . . . . . . . . . .   9
   4.  Guidelines for Provisional URI Scheme Registration  . . . . .   9
   5.  Guidelines for Historical URI Scheme Registration . . . . . .  10
   6.  Guidelines for Private URI Scheme Use . . . . . . . . . . . .  10
   7.  URI Scheme Registration Procedure . . . . . . . . . . . . . .  10
     7.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.2.  Registration Procedures . . . . . . . . . . . . . . . . .  10
     7.3.  Change Control  . . . . . . . . . . . . . . . . . . . . .  13
     7.4.  URI Scheme Registration Template  . . . . . . . . . . . .  13
   8.  The "example" URI Scheme  . . . . . . . . . . . . . . . . . .  14
     8.1.  "Example" URI Scheme Registration Request . . . . . . . .  15
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  16
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  16
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     12.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Appendix A.  Changes Since RFC 4395 . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   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.

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   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, as well as a 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:

   o  provide a central point of discovery for established URI scheme
      names, and easy location of defining documents for schemes;

   o  discourage multiple separate uses of the same scheme name;

   o  help those proposing new scheme names to discern established
      trends and conventions, and avoid names that might be confused
      with existing ones;

   o  encourage registration by setting a low barrier for registration.

1.1.  URIs and IRIs

   As originally defined, URIs only allowed a limited repertoire of
   characters chosen from US-ASCII.  An Internationalized Resource
   Identifier (IRI), as defined by [RFC3987], extends the URI syntax to
   allow characters from a much greater repertoire, to accommodate
   resource identifiers from the world's languages.  RFC 3987 [RFC3987]
   also defined a mapping between URIs and IRIs.  IRIs use the same
   scheme names as URIs.  Thus, there is no separate, independent
   registry or registration process for IRI schemes: the URI Schemes
   registry is used for both URIs and IRIs.  Those who wish to describe
   resource identifiers that are useful as IRIs should define the
   corresponding URI syntax, and note that the IRI usage follows the
   rules and transformations defined in [RFC3987].

2.  Terminology

   Within this document, the key words MUST, MAY, SHOULD, REQUIRED,
   RECOMMENDED, and so forth are used within the general meanings
   established in [RFC2119], as requirements on future registrations.

   This document distinguishes between a "scheme specification", being a
   document defining the syntax and semantics of a scheme, vs. a "scheme

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   registration request" being the completed template submitted to IANA.
   The term "scheme definition" refers generically to the syntax and
   semantics of a scheme, typically documented in a scheme
   specification.

3.  Requirements for Permanent Scheme Definitions

   This section gives considerations for new schemes.  Meeting these
   guidelines is REQUIRED for permanent scheme registration.  Permanent
   status is appropriate for, but not limited to, use in standards.  For
   URI schemes defined or normatively referenced by IETF Standards-Track
   documents, Permanent registration status is REQUIRED.

   [RFC3986] defines the overall syntax for URIs as:

               URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]

   A scheme definition cannot override the overall syntax for URIs.  For
   example, this means that fragment identifiers cannot be re-used
   outside the generic syntax restrictions, and fragment identifiers are
   not scheme-specific.  A scheme definition must specify the scheme
   name and the syntax of the scheme-specific part, which is clarified
   as follows:

                 URI = scheme ":" scheme-specific-part [ "#" fragment ]

                 scheme-specific-part = hier-part [ "?" query ]

3.1.  Demonstrable, New, Long-Lived Utility

   In general, the use and deployment of new schemes in the Internet
   infrastructure can be costly; some parts of URI processing are often
   scheme-dependent.  Introducing a new scheme might require additional
   software, not only for client software and user agents but also in
   additional parts of the network infrastructure (gateways, proxies,
   caches) [W3CWebArch].  Since scheme names share a single, global
   namespace, it is desirable to avoid contention over use of short,
   mnemonic scheme names.  New schemes ought to have utility to the
   Internet community beyond that available with already registered
   schemes.  The scheme specification SHOULD discuss the utility of the
   scheme being registered.

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3.2.  Syntactic Compatibility

   [RFC3986] defines the generic syntax for all URI schemes, along with
   the syntax of common URI components that are used by many URI schemes
   to define hierarchical identifiers.  [RFC3987] extended this generic
   syntax to cover IRIs.  All scheme specifications MUST define their
   own URI <scheme-specific-part> syntax.  Care must be taken to ensure
   that all strings matching their scheme-specific syntax will also
   match the <absolute-URI> grammar described in [RFC3986].

   New schemes SHOULD reuse the common URI components of [RFC3986] for
   the definition of hierarchical naming schemes.  If there is a strong
   reason for a scheme not to use the hierarchical syntax, then the new
   scheme definition SHOULD follow the syntax of similar previously
   registered schemes.

   Schemes that are not intended for use with relative URIs SHOULD avoid
   use of the forward slash "/" character, in order to avoid unintended
   processing such as resolution of "." and ".." (dot-segments).

   Schemes SHOULD avoid improper use of "//".  The use of double slashes
   in the first part of a URI is not a stylistic indicator that what
   follows is a URI: Double slashes are intended for use ONLY when the
   syntax of the <scheme-specific-part> contains a hierarchical
   structure.  In URIs from such schemes, the use of double slashes
   indicates that what follows is the top hierarchical element for a
   naming authority.  (Section 3.2 of RFC 3986 has more details.)
   Schemes that do not contain a conformant hierarchical structure in
   their <scheme-specific-part> SHOULD NOT use double slashes following
   the "<scheme>:" string.

   New schemes SHOULD clearly define the role of reserved characters
   (see [RFC3986], Section 2.2) in URIs of the scheme being defined.
   The syntax of the new scheme should be clear about which of the
   "reserved" set of characters are used as delimiters within the URIs
   of the new scheme, and when those characters must be escaped, versus
   when they can be used without escaping.

3.3.  Well-Defined

   While URIs might or might not be defined as locators in practice, a
   scheme definition itself MUST be clear as to how it is expected to
   function.  Schemes that are not intended to be used as locators
   SHOULD describe how the resource identified can be determined or
   accessed by software that obtains a URI of that scheme.

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   For schemes that function as locators, it is important that the
   mechanism of resource location be clearly defined.  This might mean
   different things depending on the nature of the scheme.

   In many cases, new schemes are defined as ways to translate between
   other namespaces or protocols and the general framework of URIs.  For
   example, the "ftp" scheme translates into the FTP protocol, while the
   "mid" scheme translates into a Message-ID identifier of an email
   message.  For such schemes, the description of the mapping MUST be
   complete, and in sufficient detail so that the mapping in both
   directions is clear: how to map from a URI into an identifier or set
   of protocol actions or name in the target namespace, and how legal
   values in the base namespace, or legal protocol interactions, are
   represented in a valid URI.  See Section 3.6 for guidelines for
   encoding strings or sequences of bytes within valid character
   sequences in a URI.  If not all legal values or protocol interactions
   of the base standard can be represented using the scheme, the
   definition SHOULD be clear about which subset is allowed, and why.

3.4.  Definition of Operations

   As part of the definition of how a URI identifies a resource, a
   scheme definition SHOULD define the applicable set of operations that
   can be performed on a resource using the URI as its identifier.  A
   model for this is HTTP methods; an HTTP resource can be operated on
   by GET, POST, PUT, and a number of other methods available through
   the HTTP protocol.  The scheme definition SHOULD describe all well-
   defined operations on the resource identifier, and what they are
   supposed to do.

   Some schemes don't fit into the "information access" paradigm of
   URIs.  For example, "telnet" provides location information for
   initiating a bi-directional data stream to a remote host; the only
   operation defined is to initiate the connection.  In any case, the
   operations appropriate for a scheme SHOULD be documented.

   Note: It is perfectly valid to say that "no operation apart from GET
   is defined for this URI".  It is also valid to say that "there's only
   one operation defined for this URI, and it's not very GET-like".  The
   important point is that what is defined on this scheme is described.

   Scheme definitions SHOULD define a "default" operation for when a URI
   is invoked (or "dereferenced") by an application.  For example, a
   common "default" operation today is to launch an application
   associated with the scheme name, and let it use the other URI
   components as inputs to do something.  The default invocation, or
   dereferencing, of a URI SHOULD be "safe" in the sense described by

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   section 3.4 of [W3CWebArch]; i.e., performing such an invocation
   should not incur any additional obligations by doing so.

3.5.  Context of Use

   In general, URIs are used within a broad range of protocols and
   applications.  For example, URIs are commonly used within hypertext
   documents as references to other resources.  In some cases, a scheme
   is intended for use within a different, specific set of protocols or
   applications.  If so, the scheme definition SHOULD describe the
   intended use and include references to documentation that define the
   applications and/or protocols cited.

3.6.  Internationalization and Character Encoding

   When describing schemes in which (some of) the elements of the URI
   are actually representations of human-readable text, care should be
   taken not to introduce unnecessary variety in the ways in which
   characters are encoded into octets and then into URI characters; see
   [RFC3987] and Section 2.5 (especially the last paragraph) of
   [RFC3986] for guidelines.  If URIs of a scheme contain any text
   fields, the scheme definition MUST describe the ways in which
   characters are encoded and any compatibility issues with IRIs of the
   scheme.

   The scheme specification SHOULD be as restrictive as possible
   regarding what characters are allowed in the URI, because some
   characters can create several different security issues (see, for
   example [RFC4690]).

   All percent-encoded variants are automatically included by definition
   for any character given in an IRI production.  This means that if you
   want to restrict the URI percent-encoded forms in some way, you must
   restrict the Unicode forms that would lead to them.  In most cases,
   it is advisable to define the actual characters allowed in an IRI
   production, to allow the 'pct-encoded' definition from Section 2.1 of
   [RFC3986] at the same places, and to add prose that limits percent-
   escapes to those that can be created by converting valid character
   sequences to percent-encoding via UTF-8.

3.7.  Clear Security Considerations

   Definitions of schemes MUST be accompanied by a clear analysis of the
   security implications for systems that use the scheme; this follows
   the practice of Security Consideration sections within IANA
   registrations [RFC5226].

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   In particular, Section 7 of RFC 3986 [RFC3986] describes general
   security considerations for URIs, while [RFC3987] gives those for
   IRIs.  The definition of an individual scheme should note which of
   these apply to the specified scheme, in addition to any more scheme-
   specific concerns.

3.8.  Scheme Name Considerations

   Section 3.1 of RFC 3986 defines the syntax of a URI scheme name; this
   syntax remains the same for IRIs.  New scheme registrations MUST
   follow this syntax, which only allows a limited repertoire of
   characters (taken from US-ASCII).  Although the syntax for the scheme
   name in URIs is case insensitive, the scheme name itself MUST be
   registered using lowercase letters.

   Scheme names SHOULD be short, but also sufficiently descriptive and
   distinguished to avoid problems.

   Schemes SHOULD NOT use names or other symbols that might cause
   problems with rights to use the name in IETF specifications and
   Internet protocols.  For example, be careful with trademark and
   service mark names.  (See Section 7.4 of [RFC3978].)

   Schemes SHOULD NOT use names that are either very general purpose or
   associated in the community with some other application or protocol.
   Schemes also SHOULD NOT use names that are overly general or
   grandiose in scope (e.g., that allude to their "universal" or
   "standard" nature.)

   A scheme name is not a "protocol."  However, like a service name as
   defined in section 5 of [RFC6335], it often identifies a particular
   protocol or application.  If a scheme name has a one-to-one
   correspondence with a service name, then the names SHOULD be the
   same.

   Some organizations desire their own namespace for URI scheme names
   for private use (see Section 6).  In doing so, it is important to
   prevent collisions, and to make it possible to identify the owner of
   a private use scheme.  To accomplish these two goals, such
   organizations SHOULD use a prefix based on their domain name,
   expressed in reverse order.  For example, a URI scheme name of
   com.example.info might be used by the organization that owns the
   example.com domain name.  Care must be taken, however, if the
   organization later loses the domain name embedded in their scheme
   names, since domain name registrations are not permanent.  To
   associate the private use scheme name with the original organization,
   the private use scheme can be registered using the registration
   procedure in Section 7.

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   Furthermore, to prevent collisions with private use scheme names, new
   scheme names registered MUST NOT contain a "." unless actually
   constructed from a reversed domain name.

3.9.  Interoperability Considerations

   If the person or group registering the scheme is aware of any details
   regarding the scheme that might impact interoperability, identify
   them.  For example: proprietary or uncommon encoding methods;
   incompatibility with types or versions of any underlying protocol.

4.  Guidelines for Provisional URI Scheme Registration

   Provisional registration can be used for schemes that are not part of
   any standard, but that are intended for use (or observed to be in
   use) that is not limited to a private environment within a single
   organization.  Provisional registration can also be used as an
   intermediate step on the way to permanent registration, e.g., before
   the scheme specification is finalized as a standard.

   For a provisional registration, the following are REQUIRED:

   o  The scheme name meets the syntactic requirements of Section 3.8.

   o  There must not already be an entry with the same scheme name.  In
      the unfortunate case that there are multiple, different uses of
      the same scheme name, the Designated Expert can approve a request
      to modify an existing entry to note the separate use.

   o  Contact information identifying the person supplying the
      registration is included.  Previously unregistered schemes
      discovered in use can be registered by third parties (even if not
      on behalf of those who created the scheme).  In this case, both
      the registering party and the scheme creator SHOULD be identified.

   o  If no permanent, citable specification for the scheme definition
      is included, credible reasons for not providing it SHOULD be
      given.

   o  The scheme definition SHOULD include clear security considerations
      (Section 3.7) or explain why a full security analysis is not
      available (e.g., in a third-party scheme registration).

   o  If the scheme definition does not meet the guidelines laid out in
      Section 3, the differences and reasons SHOULD be noted.

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5.  Guidelines for Historical URI Scheme Registration

   In some circumstances, it is appropriate to note a scheme that was
   once in use or registered but for whatever reason is no longer in
   common use or whose use is not recommended.  In this case, it is
   possible for an individual to request that the URI scheme be
   registered (newly, or as an update to an existing registration) as
   'historical'.  Any scheme that is no longer in common use MAY be
   designated as historical; the registration SHOULD contain some
   indication as to where the scheme was previously defined or
   documented.

6.  Guidelines for Private URI Scheme Use

   Unregistered schemes can cause problems if use is not limited to a
   private environment within a single organization, since the use could
   leak out beyond the closed environment.  Even within a closed
   environment, other colliding uses of the same scheme name could
   occur.  As such, a unique namespace (see Section 3.8) MUST be used,
   and it is strongly encouraged to do a Provisional registration unless
   the scheme name is constructed from a domain name as discussed in
   Section 3.8..

7.  URI Scheme Registration Procedure

7.1.  General

   The IANA policy (using terms defined in [RFC5226]) for Provisional
   registration was formerly Expert Review.  The policy for Permanent
   and Historic registration continues to be Expert Review, but this
   document changes the policy for Provisional registration to First
   Come First Served.

   The registration procedure is intended to be very lightweight for
   non-contentious registrations.  For the most part, we expect the good
   sense of submitters and reviewers, guided by these procedures, to
   achieve an acceptable and useful consensus for the community.

   In exceptional cases, where the negotiating parties cannot form a
   consensus, the final arbiter of any contested registration shall be
   the IESG.

7.2.  Registration Procedures

   Someone wishing to register a new scheme MUST:

   1.  Check the IANA URI Schemes registry to see whether there is
       already an entry for the desired name.  If there is already an

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       entry under the name, choose a different scheme name, or update
       the existing scheme specification.

   2.  Prepare a scheme registration request using the template
       specified in Section 7.4.  The scheme registration request can be
       contained in an Internet Draft, submitted alone, or as part of
       some other permanently available, stable, protocol specification.
       The scheme registration request can also be submitted in some
       other form (as part of another document or as a stand-alone
       document), but the scheme registration request will be treated as
       an "IETF Contribution" under the guidelines of [RFC3978].

   3.  If the registration request is for a Permanent registration (or,
       optionally, for any other registration if desired):

       1.  Review the requirements in Section 3.

       2.  Send a copy of the scheme registration request or a pointer
           to the containing document (with specific reference to the
           section with the scheme registration request) to the mailing
           list uri-review@ietf.org , requesting review.  In addition,
           request review on other relevant mailing lists as
           appropriate.  For example, general discussion of URI
           syntactical issues can be discussed on uri@w3.org; schemes
           for a network protocol can be discussed on a mailing list for
           that protocol.  Allow a reasonable time for discussion and
           comments.  Four weeks is reasonable for a permanent
           registration request.

       3.  Respond to review comments and make revisions to the proposed
           registration as needed to bring it into line with the
           guidelines given in this document.

   4.  Submit the (possibly updated) scheme registration request (or
       pointer to document containing it) to IANA at iana@iana.org.

   Upon receipt of a scheme registration request, the following steps
   MUST be followed:

   1.  IANA checks the submission for completeness; if required sections
       of the scheme registration request are missing or any citations
       are not correct, IANA will reject the registration request.  A
       registrant can resubmit a corrected request if desired.

   2.  If the request is for Provisional registration and no entry
       already exists in the current registry for the same name, IANA

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       adds the registration to the registry, under the First Come First
       Served policy.

   3.  Otherwise, IANA enters the registration request in the IANA
       registry, with status marked as "Pending Review", and the
       remainder of this section applies.

   4.  IANA requests Expert Review of the registration request against
       the corresponding guidelines from this document.

   5.  The Designated Expert will evaluate the request against the
       criteria of the requested status.

   6.  In the case of a Permanent registration request, the Designated
       Expert may:

       *  Accept the specification of the scheme for permanent
          registration.

       *  Suggest provisional registration instead.

       *  Request IETF review and IESG approval; in the meanwhile,
          suggest provisional registration.

       *  Request additional review or discussion, as necessary.

   7.  If an entry already exists for the same name, the Designated
       Expert will determine whether the request should be rejected, or
       whether the existing entry should be modified to note the
       separate use.  This conflict process applies regardless of the
       requested status or the status of the existing entry.

   8.  Once Expert Review approves registration for a given status, IANA
       updates the registration to indicate the approved status.  If
       Expert Review instead rejects the registration, the "Pending
       Review" request is removed from the registry.

   Either based on an explicit request or independently initiated, the
   Designated Expert or the IESG can request the upgrade of a
   'provisional' registration to a 'permanent' one.  In such cases, IANA
   will update the status of the corresponding entry.  Typically this
   would only occur if the use is considered a standard (not necessarily
   an IETF standard).

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7.3.  Change Control

   Registrations can be updated in the registry by the same mechanism as
   required for an initial registration.  In cases where the original
   definition of the scheme is contained in an IESG-approved document,
   update of the specification also requires IESG approval.

   Provisional registrations can be updated by the original registrant
   or anyone designated by the original registrant.  In addition, the
   IESG can reassign responsibility for a provisional registration
   scheme, or can request specific changes to a scheme registration.
   This will enable changes to be made to schemes where the original
   registrant is out of contact, or unwilling or unable to make changes.

   Transition from 'provisional' to 'permanent' status can be requested
   and approved in the same manner as a new 'permanent' registration.
   Transition from 'permanent' to 'historical' status requires IESG
   approval.  Transition from 'provisional' to 'historical' can be
   requested by anyone authorized to update the provisional
   registration.

7.4.  URI Scheme Registration Template

   This template describes the fields that MUST be supplied in a scheme
   registration request, suitable for adding to the registry:

   Scheme name:
     See Section 3.8 for guidelines.

   Status:
     This reflects the status requested, and must be one of 'permanent',
     'provisional', or 'historical'.

   Applications/protocols that use this scheme name:
     See Section 3.5.

   Contact:
     Person (including contact information) to contact for further
     information.

   Change controller:
     Organization or person (often the author), including contact
     information, authorized to change this.

   References:
     Include full citations for all referenced documents.  Scheme
     registration requests for provisional registration can be included
     in an Internet Draft; when the documents expire or are approved for

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     publication as an RFC, the registration will be updated.  A scheme
     specification is only required for Permanent registration.

   The previous version of this specification required the following
   additional fields in a scheme registration request.  These fields are
   no longer part of the template.  The answers instead belong in the
   scheme specification.

   Scheme syntax:
     See Section 3.2 for guidelines.

   Scheme semantics:
     See Section 3.3 and Section 3.4 for guidelines.

   Encoding considerations:
     See Section 3.3 and Section 3.6 for guidelines.

   Interoperability considerations:
     See Section 3.9 for guidelines.

   Security considerations:
     See Section 3.7 for guidelines.

8.  The "example" URI Scheme

   There is a need for a scheme name that can be used for examples in
   documentation without fear of conflicts with current or future actual
   schemes.  The scheme "example" is hereby registered as a Permanent
   scheme for that purpose.

   The "example" scheme is specified as follows:

   Scheme syntax:  The entire range of allowable syntax specified in
     [RFC3986] is allowed for "example" URIs.  Similarly, the entire
     range of allowable syntax specified in [RFC3987] is allowed for
     "example" IRIs.  For example, <example:foo>, <example:/foo>, and
     <example://foo> are all valid.

   Scheme semantics:  URIs in the "example" scheme are to be used for
     documentation purposes only.  The use of "example" URIs must not be
     used as locators, identify any resources, or specify any particular
     set of operations.

   Encoding considerations:  See Section 2.5 of [RFC3986] for
     guidelines.

   Interoperability considerations:  None.

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   Security considerations:  None.

8.1.  "Example" URI Scheme Registration Request

   Scheme name:  example

   Status:  permanent

   Applications/protocols that use this scheme name:  An "example" URI
     is to be used for documentation purposes only.  It MUST NOT be used
     for any protocol.

   Contact:  N/A

   Author/Change controller:  IETF

   References:  Section 8 of this RFC XXXX.
     RFC Editor Note: Replace XXXX with this RFC's reference.

9.  IANA Considerations

   Previously, the former "URL Scheme" registry was replaced by the
   "Uniform Resource Identifier (URI) Schemes" registry.  The process
   was based on [RFC5226] "Expert Review" with an initial (optional)
   mailing list review.

   The updated template has an additional field for the status of the
   scheme, and the procedures for entering new name schemes have been
   augmented.  Section 7 establishes the process for new scheme
   registration.

   IANA is requested to do the following:

   o  Update the URI Schemes registry to point to this document.

   o  Combine the "Permanent URI Schemes", "Provisional URI Schemes",
      and "Historical URI Schemes" sub-registries into a single common
      registry with an additional "Status" column containing the status
      (Permanent, Provisional, Historical, or Pending Review), and an
      additional "Notes" column which is normally empty, but may contain
      notes approved by the Designated Expert.

   o  Add the "example" URI scheme to the registry (see the template in
      Section 8.1 for registration).

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10.  Security Considerations

   All registered values are expected to contain clear security
   considerations as discussed in Section 3.7.  However, information
   concerning possible security vulnerabilities of a protocol might
   change over time.  Consequently, claims as to the security properties
   of a registered scheme might change as well.  As new vulnerabilities
   are discovered, information about such vulnerabilities might need to
   be attached to existing documentation, so that users are not misled
   as to the true security properties of a registered scheme.

11.  Acknowledgements

   Thanks to Mark Nottingham and Graham Klyne and other members of the
   apps-discuss@ietf.org mailing list for their comments on this
   document.

   Many thanks to Patrik Faltstrom, Paul Hoffmann, Ira McDonald, Roy
   Fielding, Stu Weibel, Tony Hammond, Charles Lindsey, Mark Baker, and
   other members of the uri@w3.org mailing list for their comments on
   earlier versions.

   Parts of this document are based on [RFC2717], [RFC2718] and
   [RFC3864].  Some of the ideas about use of URIs were taken from the
   "Architecture of the World Wide Web" [W3CWebArch].

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2141]  Moats, R., "URN Syntax", RFC 2141, May 1997.

   [RFC3978]  Bradner, S., "IETF Rights in Contributions", RFC 3978,
              March 2005.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

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   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165, RFC
              6335, August 2011.

12.2.  Informative References

   [RFC2717]  Petke, R. and I. King, "Registration Procedures for URL
              Scheme Names", BCP 35, RFC 2717, November 1999.

   [RFC2718]  Masinter, L., Alvestrand, H., Zigmond, D., and R. Petke,
              "Guidelines for new URL Schemes", RFC 2718, November 1999.

   [RFC3406]  Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
              "Uniform Resource Names (URN) Namespace Definition
              Mechanisms", BCP 66, RFC 3406, October 2002.

   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              September 2004.

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", BCP 35, RFC
              4395, February 2006.

   [RFC4690]  Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and
              Recommendations for Internationalized Domain Names
              (IDNs)", RFC 4690, September 2006.

   [W3CWebArch]
              W3C Technical Architecture Group, "Architecture of the
              World Wide Web, Volume One", December 2004,
              <http://www.w3.org/TR/webarch/>.

Appendix A.  Changes Since RFC 4395

   1.   Combined the Historical, Permanent, and Provisional URI Schemes
        registries into one registry with a status column.  This is done
        to make it easier to prevent duplicates and see existing
        conventions.

   2.   Added a Notes column in the registry for notes approved by the
        Designated Expert.

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   3.   Moved the following fields out of the scheme registration
        request template and into the requirements for a scheme
        specification: Scheme syntax, Scheme semantics, Encoding
        considerations, Interoperability considerations, and Security
        considerations.

   4.   Simplified the process for Provisional registration
        significantly: changed from Expert Review to First Come First
        Served, and clarified that mailing list review is not required.

   5.   Updated process for handling of scheme name conflicts, so that
        adding a note can be approved by the Designated Expert rather
        than the IESG.

   6.   Clarified that a "URI scheme name" and an "IRI scheme name" are
        the same thing and thus use the same IANA registry.

   7.   Clarified that a registration request falls under the "IETF
        Contribution" rules, but the scheme's specification need not.

   8.   Added the "example:" URI scheme.

   9.   Added text about when to use Provisional registration.

   10.  Updated convention for Private use schemes to use "." (instead
        of "-") between domain name labels, to reduce chance of
        collision, and recommended use of a reverse domain name prefix
        to allow identifying the owning organization.

   11.  Recommended that scheme definitions define a "default" operation
        for when a URI is invoked.

   12.  Recommended that a scheme name be the same as the service name,
        when there exists a 1:1 correspondence.

   13.  Elaborated on when a Provisional request should be upgraded to
        Permanent.

Authors' Addresses

   Dave Thaler (editor)
   Microsoft
   One Microsoft Way
   Redmond, WA  98052
   US

   Phone: +1 425 703 8835
   Email: dthaler@microsoft.com

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   Tony Hansen
   AT&T Laboratories
   200 Laurel Ave.
   Middletown, NJ  07748
   USA

   Email: tony+urireg@maillennium.att.com

   Ted Hardie
   Google

   Phone: +1 408 628 5864
   Email: ted.ietf@gmail.com

   Larry Masinter
   Adobe
   345 Park Ave.
   San Jose, CA  95110
   US

   Phone: +1 408 536 3024
   Email: masinter@adobe.com
   URI:   http://larry.masinter.net

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