Network Working Group                                         J. Holsten
Internet-Draft                                                       N/A
Intended status: Informational                                   L. Hunt
Expires: July 31, 2009                              Opera Software, ASA.
                                                        January 27, 2009

                         The 'about' URI scheme

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   This document specifies the URI (Uniform Resource Identifier) scheme

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   "about".  About URIs are designed to be an internal, application-
   level identifier.  Unlike many other URI schemes, the resolution of,
   and resources represented by, about URIs are left entirely to each
   individual application.

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 proving access to built-in functionality, such as
   application preferences and settings, information about the
   application, or "easter eggs".

   About URIs are more memorable than an equivalent urn or tag URI.
   Using an http URI would not only be less memorable, but also longer
   and semantically confusing.  While any number of existing schemes
   could be used to identify such resources, about URIs have become the
   de facto standard.  Browsers already use the about scheme.  The
   about:blank (Section 3.1) URI is ubiquitous, and some browsers also
   provide other resources with the about scheme, including those in
   Section 3.2.

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

2.  URI Syntax

   The general syntax of a about URI, in ABNF [RFC5234] is:

             abouturi = "about:" segment

   where "segment" is imported from [RFC3986].  About URIs are always
   escaped, as per [RFC3986].

   No relative URI syntax is defined.

3.  Resolving About URIs

   In general, applications are free to resolve any about URI to any
   resource, either internal or external, or redirect to an alternative
   URI, with about:blank being the only exception.

   As about URIs are designed to be internal to each application, there
   is no expectation of any URI, except about:blank, 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.

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   Because about URIs identify application specific information,
   applications should not need to retrieve remote information for such
   a resource.

   The about:blank URI is the only about URI reserved by this

3.1.  about:blank

   This URI identifies an empty resource.  If the application may use a
   document of MIME type 'text/html' and character encoding 'UTF-8',
   about:blank SHOULD be represented with an empty document.  Other
   representations are not defined.

3.2.  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.

   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

   about:internets  An easter egg supported by Google Chrome depicting
      the internet as a series of tubes.

4.  Acknowledgements

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

5.  Security Considerations

   There is no guarantee that an application will understand any about
   URI provided to it.  An about URI may not resolve to the expected
   resource.  If the reference is unlikely to resolve correctly, the
   reference should be accompanied by an explanation or alternatives.

   Some applications are known to display arbitrary HTML following the

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   scheme.  Applications should be cautious when accessing an about URI.
   An application should not execute or display information in an about
   URI.  About URIs should not cause the application to modify any data.
   Applications should not use about URIs to access, or erase files or
   other sensitive information.

   About URIs may identify resources which show sensitive information.
   This data SHOULD NOT be exposed in about URIs.>

6.  IANA Considerations

   This specification requests the IANA permanently 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 2

   URI scheme semantics:  See Section 1

   Encoding considerations:  Percent-encoding is allowed in 'segment'
      components (see Section 2)

   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.  Other about URIs should only be expected to work
      correctly within the same application.

   Security considerations:  See Section 5

   Relevant publications:  None

   Contact:  Joseph Holsten (

   Author/Change controller:  Joseph Holsten

7.  References

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7.1.  Normative References

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

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

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

7.2.  Informative References

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", BCP 115,
              RFC 4395, February 2006.

Authors' Addresses

   Joseph Anthony Pasquale Holsten


   Lachlan Hunt
   Opera Software, ASA.


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