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Internet Engineering Task Force (IETF)
Request for Comments: 6694
Category: Informational
ISSN: 2070-1721
S. Moonesamy, Ed.
August 2012

The "about" URI Scheme

Abstract

This document describes the "about" URI scheme, which is widely used by Web browsers and some other applications to designate access to their internal resources, such as settings, application information, hidden built-in functionality, and so on.

Status of This Memo

This document is not an Internet Standards Track specification; it is published for informational purposes.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6694.

Copyright Notice

Copyright © 2012 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 Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must 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
   2. URI Scheme Specification ........................................2
      2.1. URI Scheme Syntax ..........................................2
      2.2. URI Scheme Semantics .......................................3
           2.2.1. Well-Known "about" URIs .............................3
      2.3. Encoding Considerations ....................................3
   3. "about:blank" ...................................................3
   4. Security Considerations .........................................3
   5. IANA Considerations .............................................4
      5.1. URI Scheme Registration ....................................4
      5.2. A Registry for Well-Known Tokens ...........................5
           5.2.1. Registration Procedure ..............................5
   6. References ......................................................6
      6.1. Normative References .......................................6
      6.2. Informative References .....................................6
   Appendix A. Acknowledgments ........................................7

1. Introduction

This document describes the "about" Uniform Resource Identifier (URI) scheme. The "about" URI scheme is currently widely used by Web browsers to designate access to their internal resources, such as settings, application information, and so-called "Easter eggs" (i.e., a hidden feature or joke in an application).

2. URI Scheme Specification

2.1. URI Scheme Syntax

The "about" URI syntactically conforms to the <about-uri> rule below, expressed using the Augmented Backus-Naur Form (ABNF) [RFC5234]: 

     about-uri = "about:" about-token [ about-query ] [ about-fragment ]
     about-token = *pchar
     about-query = "?" query
     about-fragment = "#" fragment
     pchar     = <as specified in RFC 3986, Appendix A>
     query     = <as specified in RFC 3986, Appendix A>
     fragment  = <as specified in RFC 3986, Appendix A>

2.2. URI Scheme Semantics

The resource that is referenced by a particular "about" URI is denoted by the <about-token> part of the URI. It is not a hierarchical element for a naming authority. The <about-query> part specifies additional information about its handling and/or the information that should be returned by the resource referenced by the URI.

It is impossible to specify a binding between all the possible tokens and the semantics of "about" URIs that would contain such tokens. Therefore, the resource referenced by the URI is generally considered to be specific to a Web browser implementation.

2.2.1. Well-Known "about" URIs

Some <about-token>s have been reserved, as the behavior of the resource that is referenced is well-known (well-known tokens).

A well-known "about" URI is a URI that has a well-known token as its <about-token> part. It is recommended that such URIs be handled in accordance with the specification referenced in the "about" URI Tokens registry (see Section 5.2).

Well-known "about" URIs are intended to be registered when there is a need to codify the behavior of a particular <about-token>.

2.3. Encoding Considerations

"about" URIs are subject to encoding rules as defined in RFC 3986 [RFC3986].

3. "about:blank"

This document defines one well-known token: "blank". The "about:blank" URI refers to a resource represented in the browser by a blank page.

4. Security Considerations

Security considerations for URIs are discussed in Section 7 of RFC 3986 [RFC3986]. However, most of those provisions do not apply to the "about" URI scheme, as they are mainly scoped to schemes used in the Internet.

"about" URIs can sometimes refer to sensitive information, such as user passwords stored in a cache, or parameters that, if changed, could affect a user's data. The application therefore needs to ensure that the user's data is secured and no threats are imposed by "about" URIs.

5. IANA Considerations

5.1. URI Scheme Registration

The "about" URI scheme has been registered in the "Permanent URI Schemes" registry. The information below is provided according to the guidelines from RFC 4395 [RFC4395]:

URI scheme name: about

Status: 

              Permanent

URI scheme syntax: See Section 2.1 of RFC 6694.

URI scheme semantics: See Section 2.2 of RFC 6694.

URI scheme encoding considerations: See Section 2.3 of RFC 6694.

Applications that use the scheme: "about" URIs are predominantly

used by Web browsers.

Security considerations: See Section 4 of RFC 6694.

Contact: IETF Applications Area Directors 

         <app-ads@tools.ietf.org>
      
      Author/Change controller: IESG <iesg@ietf.org> (on behalf of the
         IETF)

References:

See Section 6 of RFC 6694.

5.2. A Registry for Well-Known Tokens

This document creates the '"about" URI Tokens' registry.

The registry entries consist of three fields: Token, Description, and Reference. The Token field has to conform to <about-token> production as defined in Section 2.1. The initial assignment is as follows: 

   +--------------+------------------------------------+-------------+
   | Token        | Description                        | Reference   |
   +--------------+------------------------------------+-------------+
   | blank        | The about:blank URI references a   | RFC 6694    |
   |              | blank page.                        |             |
   +--------------+------------------------------------+-------------+

5.2.1. Registration Procedure

The registration policy for this registry is "First Come First Served", as described in RFC 5226 [RFC5226]. The registrant of the token should provide the information mentioned in the following registration template: 

   o  Registered token:  The desired well-known token to be used in
   
      "about" URIs.
   
   o  Intended usage:  A short description of how "about" URIs with the
      registered token are handled, including information about the
      referenced resource.
   
   o  Contact/change controller:  Person (including contact information)
      authorized to change this registration.
   
   o  Specification:  A stable reference to a document that specifies
      the registered "about" URI.  The question of interoperability does
      not arise.  The key motivation is to have a reference to a
      specification documenting well-known behavior of the "about" URI
      in Web browsers.  As a rule of thumb, if the behavior is common to
      two or more Web browser implementations, it can be considered
      well-known.  An existing assignment may be duplicated if the
      registered token is used in more than one Web browser
      implementation.

The following is a template for the "blank" token: 

   o  Registered token:  blank
   
   o  Intended usage:  The about:blank URI references a blank page.
   
   o  Contact/change controller:  IESG <iesg@ietf.org> (on behalf of the
      IETF).
   
   o  Specification:  RFC 6694

6. References

6.1. Normative References

   [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.
   
   [RFC5234]   Crocker, D., Ed., and P. Overell, "Augmented BNF for
               Syntax Specifications: ABNF", STD 68, RFC 5234,
               January 2008.

6.2. Informative References

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

Appendix A. Acknowledgments

This document was formed from a previous draft document initially authored by Lachlan Hunt and Joseph Holsten. Additionally, the contributions of Frank Ellermann and Alexey Melnikov are gratefully acknowledged. Barry Leiba and Murray Kucherawy deserve special credit for providing a great amount of text that was used in this document.

Lachlan Hunt and Mykyta Yevstifeyev edited previous versions of this document. Tim Bray and John Klensin provided suggestions about how to improve the document.

Author's Address

S. Moonesamy (editor)
76 Ylang Ylang Avenue
Quatre Bornes
Mauritius 

   EMail: sm+ietf@elandsys.com