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HTTP Working Group                                     Koen Holtman, TUE
Internet-Draft                              Andrew Mutz, Hewlett-Packard
Expires: January 7, 1998                                    July 7, 1997

                    Feature Tag Registration Procedures

                     draft-ietf-http-feature-reg-01.txt


STATUS OF THIS MEMO

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ABSTRACT

   Recent Internet applications, such as the World Wide Web, tie
   together a great diversity in data formats, client and server
   platforms, and communities.  This has created a need for various
   kinds of negotiation mechanisms, which tailor the data which is
   exchanged, or the exchange process, to the capabilities and
   preferences of the parties involved.

   Extensible negotiation mechanisms need a vocabulary to identify
   various things which can be negotiated on.  To promote
   interoperability, a registration process is needed to ensure that
   that this vocabulary, which can be shared between negotiation
   mechanisms, is developed in an orderly, well-specified, and public
   manner.

   This document defines registration procedures which use the
   Internet Assigned Numbers Authority (IANA) as a central registry
   for this vocabulary, which is the vocabulary of feature tags.

TABLE OF CONTENTS

   1 Introduction

   2 Basic concepts and definitions
    2.1 Dimensions of negotiation
    2.2 Feature tags
    2.3 Feature tag syntax

   3 Feature tag registration
    3.1 Registration trees
    3.1.1 IETF tree
    3.1.2 Global tree
    3.1.3 Local or specialized tree
    3.1.4 Special `x.' tree
    3.1.5 Additional registration trees
    3.2 Registration requirements
    3.2.1 Functionality requirement
    3.2.2 Naming requirements
    3.2.3 Dimension specification requirements
    3.2.4 Value canonicalization requirements
    3.2.5 Interchange recommendations
    3.2.6 Security requirements
    3.2.7 Publication requirements
    3.3 Registration procedure
    3.3.1 Present the feature tag to the community for review
    3.3.2 IESG approval
    3.3.3 IANA registration
    3.3.4 Delayed publication
    3.4 Comments on feature tag registrations
    3.5 Location of registered feature tag list
    3.6 IANA procedures for registering feature tags
    3.7 Change control
    3.8 Registration template

   4 Security considerations

   5 Acknowledgments

   6 References

   7 Authors' addresses

   Appendix A: IANA and RFC editor to-do list


1 Introduction

   Recent Internet applications, such as the World Wide Web, tie
   together a great diversity in data formats, client and server
   platforms, and communities.  This has created a need for various
   kinds of negotiation mechanisms, which tailor the data which is
   exchanged, or the exchange process itself, to the capabilities and
   preferences of the parties involved.

   Extensible negotiation mechanisms need a vocabulary to identify
   various things which can be negotiated on.  To promote
   interoperability, a registration process is needed to ensure that
   that this vocabulary, which can be shared between negotiation
   mechanisms, is developed in an orderly, well-specified, and public
   manner.

   This document defines registration procedures which use the
   Internet Assigned Numbers Authority (IANA) as a central registry
   for this vocabulary, which is the vocabulary of feature tags.


2 Basic concepts and definitions

2.1 Dimensions of negotiation

   Negotiation can be done on many things, and sometimes negotiation
   must be done on multiple things at the same time.  For example, in
   a World Wide Web application, a negotiation process might need to
   simultaneously select an appropriate media type and an appropriate
   language for the page which is to be transmitted.

   Such negotiation on multiple things can be seen as searching
   process, in which a permitted or optimal point has to be found in a
   multi-dimensional solution space.

   Dimensions can be simple, usually reflecting a simple yes/no
   choice, or more complex, reflecting a choice among many potential
   alternatives, for example the choice of a particular media type.


2.2 Feature tags

   A feature tag identifies a single dimension of negotiation, i.e.
   something which can be negotiated on.  Examples of things which can
   be negotiated on are:

     * the MIME media type of the data which is transmitted
     * the language of the text document which is transmitted
     * the color depth of the screen on which something is to be
       displayed
     * whether the recipient supports the `floating 5 dimensional
       tables' feature
     * the fonts which are available to the recipient
     * whether a Web user prefers speed over graphical detail
     * whether the recipient is capable of displaying graphical
       content
     * whether the user prefers a blue background with purple dots over
       a green background with pictures of small furry animals, except
       on Fridays.

   It is expected that the majority of feature tags will label
   features in protocols or applications, the use of which needs to be
   negotiated on.  This explains the name `feature tag'.

   It is recognized that there is continuous growth in the number of
   things for which some form of negotiation is desirable, in
   particular because there is continuous growth in the feature set of
   Internet software.  By using the feature tag vocabulary, rather
   than an internal set of hard-coded values, to identify dimensions,
   negotiation mechanisms can keep up with this growth.

   To avoid the duplication of work, and to promote the interoperable
   naming of areas of negotiation across protocols and applications,
   the feature tag namespace is not bound to a particular protocol or
   negotiation mechanism.

   The procedures in this document place no prior restriction on the
   things which may be identified by a feature tag, other than that it
   must be conceivable to negotiate on them in some Internet
   application.


2.3 Feature tag syntax

   A feature tag is a non-empty string consisting of printable
   US-ASCII characters except the space (octets 33 - 127), and except
   the reserved characters below:

              ! " * , / : ; = ? @ \

              ( ) < > [ ] { }

   Feature tags are case-insensitive.


3 Feature tag registration

   Registration of a new feature tag starts with the construction of a
   registration proposal.  Registration may occur in several different
   registration trees, which have different requirements as discussed
   below.  In general, the new registration proposal is circulated and
   reviewed in a fashion appropriate to the tree involved.  The
   feature tag is then registered if the proposal is acceptable.  The
   following sections describe the requirements and procedures used
   for each of the different registration trees.


3.1 Registration trees

   The following subsections define registration "trees",
   distinguished by the use of faceted names (e.g., names of the form
   "tree.feature_name").


3.1.1 IETF tree

   The IETF tree is intended for feature tags of general interest to
   the Internet Community.  Registration in the IETF tree requires
   approval by the IESG and publication of the feature tag
   specification as some form of RFC.

   Feature tags in the IETF tree normally have names that are not
   explicitly faceted, i.e., do not contain period (".", full stop)
   characters.

   The "owner" of a feature tag in the IETF tree is assumed to be the
   IETF itself.  Modification or alteration of the specification
   requires the same level of processing (e.g. standards track)
   required for the initial registration.

3.1.2 Global tree

   The global tree is intended for feature tags of general interest to
   the Internet Community.  Unlike registration in the IETF tree,
   registration in the global tree does not require approval by the
   IESG.  A registration may be placed in the global tree by anyone
   who has the need to allow for feature negotiation on a particular
   capability or preference.

   Typically, if the creator of an Internet service or product
   introduces something new to the Internet Community, and if it is
   meaningful to do negotiation on it, the vendor can register a
   feature tag in the global tree.

   The owner of "global" tags and associated specifications is the
   person or entity making the registration, or one to whom
   responsibility has been transferred as described below.

   Tags in the global tree will be distinguished by the leading facet
   "g.". That may be followed, at the discretion of the registration,
   by either a designation of a dimension of negotiation, (e.g.,
   "g.blinktags") or by an IANA-approved designation of the producer's
   name which is then followed by a designation of a dimension (e.g.,
   g.bigcompany.obscurefeature).

   While public exposure and review of feature tags to be registered
   in the global tree is not required, using the ietf-feature-tags
   list for review is strongly encouraged to improve the quality of
   those specifications.  Registrations in the global tree may be
   submitted directly to the IANA.

3.1.3 Local or specialized tree

   The local tree is intended for feature tags identifying dimensions
   of negotiation which are relevant in a localized, specialized,
   restricted, or experimental context.

   The owner of "local" tags and associated specifications is the
   person or entity making the registration, or one to whom
   responsibility has been transferred as described below.

   Tags in the local tree will be distinguished by the leading facet
   "l.".  While public exposure and review of feature tags to be
   registered in the local tree is not required, using the
   ietf-feature-tags list for review is strongly encouraged to improve
   the quality of those specifications.  Registrations in the local
   tree may be submitted directly to the IANA.

3.1.4 Special `x.' tree

   Feature tags with "x." as the first facet are reserved for use in
   experimental contexts.  These tags are unregistered, experimental,
   and should be used only with the active agreement of the parties
   exchanging them.

   However, with the simplified registration procedures described
   above for vendor and personal trees, it should rarely, if ever, be
   necessary to use unregistered experimental tags, and as such use of
   these tags is discouraged.

3.1.5 Additional registration trees

   From time to time and as required by the community, the IANA may,
   with the advice and consent of the IESG, create new top-level
   registration trees.  It is explicitly assumed that these trees may
   be created for external registration and management by well-known
   permanent bodies, such as scientific societies for media types
   specific to the sciences they cover.  In general, the quality of
   review of specifications for one of these additional registration
   trees is expected to be equivalent to that which IETF would give to
   registrations in its own tree.  Establishment of these new trees
   will be announced through RFC publication approved by the IESG.


3.2 Registration requirements

   Feature tag registration proposals are all expected to conform to
   various requirements laid out in the following sections.  Note that
   requirement specifics sometimes vary depending on the registration
   tree, again as detailed in the following sections.

3.2.1 Functionality requirement

   A feature tag must function as an actual identifier of a dimension
   of negotiation.  Registration of things which are better thought of
   as individual values on the axis corresponding to a dimension of
   negotiation, for example media types or character sets, is not
   allowed.

   This requirement applies regardless of the registration tree
   involved.

3.2.2 Naming requirements

   All feature tag names must be unique, and must conform to the
   syntax in section 2.3.

   This requirement applies regardless of the registration tree
   involved.

   The IANA may reject tag names which are obviously bogus or
   misleading.  Note however that other than in the IETF tree, the
   acceptance of a feature tag does not imply certification that the
   tag is adequately named.

3.2.3 Dimension specification requirements

   If a feature tag is registered in the IETF tree, a precise and
   openly available specification of the indicated dimension of
   negotiation is required, and must at a minimum be referenced by, if
   it isn't actually included in, the feature tag registration
   proposal itself.  For the global and local trees, an openly
   available description of the dimension is minimally required.

   Regardless of the tree, the specification of a feature tag must
   state whether the choice in the indicated dimension is a simple
   yes/no choice, or if it is a choice for a single value among
   multiple values.

   If the choice in the indicated dimension is among multiple values,
   and the tag is registered in the IETF tree, a precise and openly
   available specification of the exact meaning of these values is
   required, and must at a minimum be referenced by, if it isn't
   actually included in, the feature tag registration proposal itself.
   For the global and local trees, an openly available description of
   the meaning is minimally required.

   If the registration is motivated by the creation of a new feature
   in a product, it is specifically permitted to name the product
   involved, and the product version number for which the feature was
   or will be first implemented.

   The registration of feature tags referencing patented technology is
   specifically permitted.  However the restrictions set forth in RFC
   1602 on the use of patented technology in standards-track protocols
   must be respected when the specification of a feature tag is part
   of a standards-track protocol.

3.2.4 Value canonicalization requirements

   If the choice in the dimension indicated by the feature tag is
   among multiple values, and these values are not integers, and the
   tag is registered in the IETF tree, a precise and openly available
   specification of a canonical format for these values is required,
   and must at a minimum be referenced by, if it isn't actually
   included in, the feature tag registration proposal itself.  For the
   global and local trees, an openly available description of the
   canonical format is minimally required.  Regardless of the tree, it
   must be possible to map the canonical format onto octet strings.

3.2.5 Interchange recommendations

   Feature tags should, whenever possible, interoperate across as many
   systems, applications, and negotiation mechanisms as possible.
   However, some feature tags will by nature be bound to specific
   systems, and feature tag may indicate dimensions in which the
   choice is made among types of values which can only be handled by
   highly specialized negotiation mechanisms.

   Universal interoperability of feature tags is not required, but
   known interoperability issues should be identified whenever
   possible.  Publication of a feature tag does not require an
   exhaustive review of interoperability, and the interoperability
   considerations section is subject to continuing evaluation.

   These recommendations apply regardless of the registration tree
   involved.

3.2.6 Security requirements

   An analysis of security issues is required for all feature tags
   registered in the IETF tree.  (This is in accordance with the basic
   requirements for all IETF protocols.)  A similar analysis for
   feature tags registered in the global or local trees is encouraged
   but not required.  All descriptions of security issues must be as
   accurate as possible regardless of registration tree.  In
   particular, a statement that there are "no security issues
   associated with the indicated feature tag" must not be confused
   with "the security issues associates with this feature tag have not
   been assessed".

   There is absolutely no requirement that systems which negotiate
   using the feature tags registered in any tree be secure or
   completely free from risks.  Nevertheless, all known security risks
   must be identified in the registration of a feature tag, again
   regardless of registration tree.

   The security considerations section of all registrations is subject
   to continuing evaluation and modification, and in particular may be
   extended by use of the "comments on feature tags" mechanism
   described in subsequent sections.

3.2.7 Publication requirements

   Proposals for feature tags registered in the IETF tree must be
   published as RFCs.  RFC publication of global and local feature tag
   proposals is not required.  In all cases the IANA will retain
   copies of all feature tag proposals and "publish" them as part of
   the feature tag registration tree itself.

   Other than in the IETF tree, the registration of a feature tag does
   not imply endorsement, approval, or recommendation by the IANA or
   the IETF or even certification that the specification is adequate.

   It is neither possible nor necessary for the IANA to conduct a
   comprehensive review of feature tag registrations.  Nevertheless,
   the IANA has the authority to identify obviously incompetent
   material and exclude it.


3.3 Registration procedure

   The following procedure has been implemented by the IANA for review
   and approval of new feature tags.  This is not a formal standards
   process, but rather an administrative procedure intended to allow
   community comment and sanity checking without excessive time delay.
   For registration in the IETF tree, the normal IETF processes should
   be followed, treating posting of an internet-draft and announcement
   on the ietf-types list (as described in the next subsection) as a
   first step.  For registrations in the global or local trees, the
   initial review step described below may be omitted and the tag
   registered directly by submitting the template and an explanation
   to the IANA (at iana@isi.edu).  However, authors of global or local
   feature tag specifications are encouraged to seek community review
   and comment whenever that is feasible.

3.3.1 Present the feature tag to the community for review

   Send a proposed feature tag registration to the
   "ietf-feature-tags@iana.org" mailing list for a two week review
   period.  This mailing list has been established for the purpose of
   reviewing proposed feature tags.  Proposed feature tags are not
   formally registered and must not be used; the "x." prefix can be
   used until registration is complete.

   The intent of the public posting is to solicit comments and
   feedback on the choice of tag name, the clarity of the tag
   specification, and a review of any interoperability or security
   considerations.  The submitter may submit a revised registration
   proposal, or withdraw the registration proposal completely, at any
   time.

3.3.2 IESG approval

   Feature tags registered in the IETF tree must be submitted to
   the IESG for approval.

3.3.3 IANA registration

   Provided that the proposed tag meets the requirements for feature
   tags and has obtained whatever approval is necessary, the
   author may submit the registration request to the IANA, which
   will register the feature tag and make the feature tag
   registration available to the community.

3.3.4 Delayed publication

   By default, feature tag registration proposals are published by the
   IANA immediately after registration of the tag.

   In some situations, a vendor may not wish that a specification of a
   tag for a planned new feature is published before the date at which
   the software implementing this feature is released to the Internet
   Community.  Therefore, when submitting a feature tag registration
   proposal for a planned feature, a vendor may request a publication
   delay of up to two months after registration of the tag by the
   IANA.  After registration, IANA will delay its publication of the
   registration proposal for at least the duration of the requested
   period.

   Immediately after receiving a notification of registration from the
   IANA, the vendor may release software which recognizes the tag to
   the Internet Community, and make public the tag specification
   though his own channels.


3.4 Comments on feature tag registrations

   Comments on registered feature tags may be submitted by members of
   the community to the IANA.  These comments will be passed on to the
   "owner" of the feature tag if possible.  Submitters of comments may
   request that their comment be attached to the feature tag
   registration itself, and if the IANA approves of this the comment
   will be made accessible in conjunction with the tag registration
   itself.


3.5 Location of registered feature tag list

   Feature tag registrations will be posted in the anonymous FTP
   directory "ftp://ftp.isi.edu/in-notes/iana/assignments/feature-
   tags/" and all registered feature tags will be listed in the
   periodically issued "Assigned Numbers" RFC [currently STD 2,
   RFC-1700].  The feature tag description and other supporting
   material may also be published as an Informational RFC by sending
   it to "rfc-editor@isi.edu" (please follow the instructions to RFC
   authors [RFC-1543]).


3.6 IANA procedures for registering feature tags

   The IANA will only register feature tags in the IETF tree in
   response to a communication from the IESG stating that a given
   registration has been approved.

   Global and local tags will be registered by the IANA automatically
   and without any formal review as long as the following minimal
   conditions are met:

    (1)   A feature tag must function as an actual identifier of a dimension
          of negotiation.

    (2)   All feature tag names must be unique, and must conform to the
          syntax in section 2.3.

    (3)   An openly available description of the dimension is minimally
          required.  The specification of a feature tag must state
          whether the choice in the indicated dimension is a simple
          yes/no choice, or if it is a choice for a single value among
          multiple values.  If the choice is among multiple values, an
          an openly available description of the meaning of these
          values is minimally required.

    (4)   Any security considerations given must not be obviously
          bogus. (It is neither possible nor necessary for the
          IANA to conduct a comprehensive security review of
          feature tag registrations.  Nevertheless, the IANA has
          the authority to identify obviously incompetent material
          and exclude it.)


3.7 Change control

   Once a feature tag has been published by the IANA, the owner may
   request a change to its definition.  The descriptions of the
   different registration trees above designate the "owners" of each
   type of registration.  The change request follows the following
   procedure:

    (1) Publish the revised template on the ietf-feature-tags list.

    (2) Leave at least two weeks for comments.

    (3) Publish using the IANA after formal review if required.

   Changes should be requested only when there are serious omissions
   or errors in the published specification.  When review is required,
   a change request may be denied if it renders a use of tags that was
   valid under the previous definition invalid under the new
   definition.

   The owner of a feature tag may pass responsibility for the feature
   tag to another person or agency by informing the IANA and the
   ietf-feature-tags list; this can be done without discussion or
   review.

   The IESG may reassign responsibility for a feature tag.  The most
   common case of this will be to enable changes to be made to tags
   where the author of the registration has died, moved out of contact
   or is otherwise unable to make changes that are important to the
   community.

   Feature tag registrations may not be deleted; feature tags which
   are no longer believed appropriate for use can be declared OBSOLETE
   by a change to their "intended use" field; such feature tags will
   be clearly marked in the lists published by the IANA.


3.8 Registration template

   To: ietf-feature-tags@iana.org (Feature tags mailing list)
        (or directly to iana@iana.org)
   Subject: Registration of feature tag XXXX

    | Instructions are preceded by `|'.  Some fields are optional.

   Feature tag name:

   Summary of the indicated dimension of negotiation:

    | Include a short (no longer than 4 lines) description or summary
    | Examples:
    |   `Negotiation on whether to use the xyzzy feature of ...'
    |   `Negotiation on the MIME media type of the data which
    |    is transmitted for ...'
    |   `Negotiation on whether to use colors in displaying ...'
    |   `Negotiation on the number of colors to use in displaying ...'

   Result in the indicated dimension of negotiation:

     [ ] 1. A yes/no choice on whether to use or enable a particular
            feature of a protocol or application
     [ ] 2. A yes/no choice for some other thing
     [ ] 3. A choice for an integer value among several
     [ ] 4. A choice for a non-integer value among several
     [ ] 5. Other

   (Only for case 1) Description of the feature which is used or
   enabled if the choice is `yes':

    | Descriptions may also reference outside material.

   (Only for case 2) Description of the effect of the 'yes' choice:

   (Only for case 2) Description of the effect of the 'no' choice:
                                                          [optional]

     | If the effect of the `no' choice is `the direct opposite of the
     | yes choice' or `nothing special happens', this description can
     | be omitted.

   (Only for cases 3-5) Description of the thing which is negotiated
   on:

   (Only for cases 3-4, and for 5 if applicable) Description of the
   meaning of the values to be chosen from:

     | If the choice is among a small set of values, the detailed
     | description could simply describe the meaning of each
     | individual value.
     | The description could also refer to another IANA registry,
     | for example the MIME media type registry.

   (Only for case 4, and for 5 if applicable) Canonical format of the
   non-integer values to be chosen from:

   Default choice (if applicable to the intended application domain):

   Tag is intended for use in the applications, protocols, services,
   or negotiation mechanisms:                             [optional]

    | For applications, also specify the number of the first version
    | which will use the tag, if applicable.

   Examples of typical use:                               [optional]

   Related standards or documents:                        [optional]

   Considerations particular to use in individual applications,
   protocols, services, or negotiation mechanisms:        [optional]

   Interoperability considerations:                       [optional]

   Security considerations:

   Additional information:                                [optional]

     Keywords:                                            [optional]

     Related feature tags:                                [optional]

     Related media types or data formats:                 [optional]

     Related HTML markup tags:                            [optional]

   Person & email address to contact for further information:

   Intended usage:

    | one of COMMON, LIMITED USE or OBSOLETE

   Author/Change controller:

   Requested IANA publication delay:                      [optional]

    | A delay may only be requested for registration in global or
    | local trees, with a maximum of two months.

   Other information:                                     [optional]

    |  Any other information that the author deems interesting may be
    |  added here.


4 Security considerations

   When used, negotiation mechanisms usually reveal some information
   about one party to other parties.  This may raise privacy concerns,
   and may allow a malicious party to make more educated guesses about
   the presence of security holes in the other party.


5 Acknowledgments

   The details of the registration procedure in this document were
   directly adapted from [1].  Much of the text in section 3 was
   directly copied from this source.

   The idea of creating a vocabulary of dimensions of negotiation,
   which is maintained in a central open registry, is due to
   discussions on extensible negotiation mechanisms in the IETF HTTP
   working group.  The authors wish to thank Larry Masinter for
   contributing to early discussions of feature tag registration.


6 References

   [1] N. Freed, J. Klensin, J. Postel, Multipurpose Internet Mail
       Extensions (MIME) Part Four: Registration Procedures.  RFC
       2048, BCP 13, Network Working Group, November 1996


7 Authors' addresses

   Koen Holtman
   Technische Universiteit Eindhoven
   Postbus 513
   Kamer HG 6.57
   5600 MB Eindhoven (The Netherlands)
   Email: koen@win.tue.nl

   Andrew H. Mutz
   Hewlett-Packard Company
   1501 Page Mill Road 3U-3
   Palo Alto CA 94304, USA
   Fax +1 415 857 4691
   Email: mutz@hpl.hp.com


Appendix A: IANA and RFC editor to-do list

   VERY IMPORTANT NOTE:  This appendix is intended to communicate
   various editorial and procedural tasks the IANA and the RFC
   Editor should undertake prior to publication of this document
   as an RFC.  This appendix should NOT appear in the actual RFC
   version of this document!

   This document refers to the feature tags mailing list
   ietf-feature-tags@iana.org.  This list does not exist at the
   present time and needs to be created.

   The ftp://ftp.isi.edu/in-notes/iana/assignments/feature-tags/" area
   does not exist at the present time and needs to be created.


Expires: January 7, 1998


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