The "safe" HTTP Preference
RFC 8674

Document Type RFC - Informational (December 2019; No errata)
Author Mark Nottingham 
Last updated 2019-12-04
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Independent Submission                                     M. Nottingham
Request for Comments: 8674                                 December 2019
Category: Informational                                                 
ISSN: 2070-1721

                       The "safe" HTTP Preference


   This specification defines a preference for HTTP requests that
   expresses a desire to avoid objectionable content, according to the
   definition of that term by the origin server.

   This specification does not define a precise semantic for "safe".
   Rather, the term is interpreted by the server and within the scope of
   each web site that chooses to act upon this information.

   Support for this preference by clients and servers is optional.

Status of This Memo

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

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not candidates for any level of Internet Standard;
   see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2019 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
   ( 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.

Table of Contents

   1.  Introduction
     1.1.  Notational Conventions
   2.  The "safe" Preference
   3.  Security Considerations
   4.  IANA Considerations
   5.  References
     5.1.  Normative References
     5.2.  Informative References
   Appendix A.  Sending the "safe" Preference from Web Browsers
   Appendix B.  Supporting the "safe" Preference on Web Sites
   Author's Address

1.  Introduction

   Many web sites have a "safe" mode to assist those who don't want to
   be exposed (or have their children exposed) to content to which they
   might object.

   However, that goal is often difficult to achieve because of the need
   to go to every web site that might be used and navigate to the
   appropriate page (possibly creating an account along the way) to get
   a cookie [RFC6265] set in the browser, for each browser on every
   device used.

   A more manageable approach is for the browser to proactively indicate
   a preference for safe content.  A user agent that supports doing so
   (whether it be an individual browser or through an operating system
   HTTP library) need only be configured once to ensure that the
   preference is advertised to a set of sites, or even all sites.

   This specification defines how to declare this desire in requests as
   an HTTP Preference [RFC7240].

   Note that this specification does not define what content might be
   considered objectionable, so the concept of "safe" is not precisely
   defined.  Rather, the term is interpreted by the server and within
   the scope of each web site that chooses to act upon this information.

   That said, the intent is to allow end users (or those acting on their
   behalf) to express a desire to avoid content that is considered
   objectionable within the cultural context of that site; usually (but
   not always), the objectionable content is content unsuitable for
   minors.  The safe preference is not intended to be used for other

   Furthermore, sending the preference does not guarantee that the web
   site will use it or that it will apply a concept of "objectionable"
   that is consistent with the requester's views.  As such, its effect
   can be described as "best effort" and not to be relied upon.  In
   other words, sending the preference is no more reliable than going to
   each web site and manually selecting a safe mode, but it is
   considerably easier.

   It is also important to note that the safe preference is not a
   reliable indicator that the end user is a child; other users might
   have a desire for unobjectionable content, and some children might
   browse without the preference being set.

   Note also that the cultural context applies to the hosting location
   of a site, the content provider, and the source of the content.  It
   cannot be guaranteed that a user agent and origin server will have
   the same view of the concept of what is objectionable.

   Simply put, it is a statement by (or on behalf of) the end user
   indicating that "if your site has a safe setting, this user is hereby
   opting into that, according to your definition of the term."
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