Network Working Group                                         J. Holsten
Intended status: Standards Track                                 L. Hunt
Expires: October 8, 2010                            Opera Software, ASA.
                                                           April 6, 2010

                         The 'about' URI scheme


   A URI using the "about:" scheme, henceforth referred to as an "about"
   URI, is designed to be used internally by applications for almost any
   desired purpose.

Editorial Note (To be removed by RFC Editor)

   Discussion of this draft should take place on the URI Review mailing
   list (

Status of This Memo

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

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Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( 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 BSD License.

1.  Introduction

   An "about" URI is designed to be used internally by applications for
   almost any desired purpose.  Such URIs have commonly been used by web
   browsers for providing access to built-in functionality, such as
   application information, preferences, settings, or "easter eggs".

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  URI Syntax

   The general syntax of an "about" URI is defined below using ABNF

                       abouturi = "about:" segment [ "?" query ]

   where "segment" and "query" are defined in [RFC3986].

4.  Encoding Considerations

   Because many characters are not permitted with this syntax, the
   "segment" and "query" elements may contain characters from the
   Unicode Character Set [UCS] as suggested by URI [RFC3986], by first
   encoding those characters as octets to the UTF-8 character encoding
   [RFC3629]; then only those octets that do not correspond to
   characters in the unreserved set should be percent-encoded.

   By using UTF-8 encoding, there are no known compatibility issues with
   mapping Internationalized Resource Identifiers to "about" URIs
   according to [RFC3987].  Since "about" URIs do not use domain names,
   "ireg-name" conversion is unnecessary.

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5.  Resolving "about" URIs

   A reserved "about" URI is one that is defined by a specification for
   a specific purpose, which MAY also be defined to be resolvable.

   An unreserved "about" URI is any other "about" URI that is not
   defined by a specification for a specific purpose, but which may be
   recognized by an application.

   An unrecognized "about" URI is an "about" URI that is not recognized
   by an application.

5.1.  Reserved "about" URIs

   Other specifications MAY reserve "about" URIs.  Applications
   attempting to resolve reserved "about" URIs that are not defined to
   be resolvable, MAY treat such URIs as being unreserved.

5.1.1.  about:blank

   The "about" URI with the segment equal to "blank" and no query
   component is reserved by this specification. i.e. "about:blank".
   Applications resolving the URI "about:blank" MUST return a resource
   of zero length, containing no data, with the media type "text/html"
   and the character encoding "UTF-8".

   Note: If a query component is provided with "about:blank", such as
   "about:blank?" or "about:blank?foo", then the URI is not considered
   to be reserved by this specification.

5.2.  Unreserved "about" URIs

   Applications MAY resolve any unreserved "about" URI to any resource,
   either internal or external, or redirect to an alternative URI.

   Note: As "about" URIs are designed to be internal to each
   application, there is no expectation of any unreserved URI returning
   the same resource among different applications.  However, it is worth
   noting that some conventions have arisen for providing particular
   functionality via common "about" URIs.

5.3.  Unrecognized "about" URIs

   Applications SHOULD resolve unrecognized "about" URIs in the same way
   as "about:blank".

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5.4.  Examples

   The following examples illustrate some known URIs supported by
   existing applications.  They are not guaranteed to be resolvable by
   every application.

   about:config  Commonly provides access to application preferences and

   about:cache  Commonly provides access to information about resources
      stored in the browsers cache.  Current Mozilla Firefox
      implementations also accept a query string to specify a specific
      device to show more information about. e.g. about:
      cache?device=offline provides details about the offline cache.

   about:plugins  Commonly provides access to information about
      installed plugins

   about:mozilla  An easter egg supported by Mozilla showing a passage
      from the fictional Book of Mozilla

   Applications are also permitted to redirect such URIs.  For example,
   Opera redirects all "about" URIs, with the exception of
   "about:blank", to the equivalent URI using their internal "opera:"
   scheme. e.g. "about:config" redirects to "opera:config".

   This is not an exhaustive list.  Many more are supported by numerous
   applications.  For more examples, consult Wikipedia's entry on the
   "about: URI Scheme" [wikiabout].

6.  Normalization

   "about" URIs use the standard URI normalization rules [RFC3986],
   specifically Simple String Comparison, Case Normalization, and
   Percent-Encoding Normalization.  For example, "about:blank",
   "about:blan%6B" and "about:blan%6b" are equivalent, though the
   percent-encoded forms are discouraged.  Due to the structure of
   "about" URIs, some normalizations do not apply, specifically Syntax-
   Based Normalization, Scheme-Based Normalization, and Protocol-Based
   Normalization.  For example, "about:blank" is not equivalent to
   "about:BLANK", "about:blank?" or "about:blank:", each may represent a
   different resource.  Similarly, "about:blank%3F" is not equivalent to

7.  Security Considerations

   Implementations of the scheme SHOULD NOT modify data when processing
   "about" resource identifiers.  Applications SHOULD NOT use "about"

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   URIs to access or erase files or other sensitive information.

   "about" URIs MAY identify resources that reveal sensitive
   information.  Applications SHOULD ensure appropriate restrictions are
   in place to protect such information from access or modification by
   untrusted sources.

8.  IANA Considerations

   This specification requests the IANA provisionally register the
   "about" URI scheme as specified in this document and summarized in
   the following template, per [RFC4395]:

   URI scheme name:  about

   Status:  Provisional

   URI scheme syntax:  See Section 3

   URI scheme semantics:  See Section 1

   Encoding considerations:  Percent-encoding is allowed in "segment"
      and "query" components.  Internationalization is handled by IRI
      processing.  See Section 4.

   Intended usage:  See Section 1

   Applications and/or protocols that use this URI scheme name:  Any
      applications that use URIs as identifiers for private resources,
      such as web browsers.

   Interoperability considerations:  Applications are only required to
      support "about:blank", and may choose to interpret other "about"
      URIs differently.

   Security considerations:  See Section 7

   Relevant publications:  None

   Contact:  Joseph Holsten (

   Author/Change controller:  Joseph Holsten

9.  Acknowledgements

   This document was made possible thanks to the input of Henri Sivonen,
   Ian Hickson, Larry Masinter, Bjoern Hoehrmann and Julian Reschke.

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10.  References

10.1.  Normative References

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

   [RFC3629]    Yergeau, F., "UTF-8, a transformation format of ISO
                10646", STD 63, RFC 3629, November 2003.

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

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

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

   [UCS]        International Organization for Standardization,
                "Information Technology - Universal Multiple-Octet Coded
                Character Set (UCS)", ISO/IEC Standard 10646,
                December 2003.

10.2.  Informative References

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

   [wikiabout]  Wikipedia, The Free Encyclopedia, "About: URI scheme".

Authors' Addresses

   Joseph Anthony Pasquale Holsten


   Lachlan Hunt
   Opera Software, ASA.


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