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Network Working Group                                           N. Freed
Request for Comments: 4288                              Sun Microsystems
BCP: 13                                                       J. Klensin
Obsoletes: 2048                                            December 2005
Category: Best Current Practice

         Media Type Specifications and Registration Procedures

Status of This Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document defines procedures for the specification and
   registration of media types for use in MIME and other Internet
   protocols.

Table of Contents

   1. Introduction ....................................................3
   2. Media Type Registration Preliminaries ...........................4
   3. Registration Trees and Subtype Names ............................4
      3.1. Standards Tree .............................................4
      3.2. Vendor Tree ................................................5
      3.3. Personal or Vanity Tree ....................................5
      3.4. Special x. Tree ............................................5
      3.5. Additional Registration Trees ..............................6
   4. Registration Requirements .......................................6
      4.1. Functionality Requirement ..................................6
      4.2. Naming Requirements ........................................6
         4.2.1. Text Media Types ......................................7
         4.2.2. Image Media Types .....................................8
         4.2.3. Audio Media Types .....................................8
         4.2.4. Video Media Types .....................................8
         4.2.5. Application Media Types ...............................9
         4.2.6. Multipart and Message Media Types .....................9
         4.2.7. Additional Top-level Types ............................9
      4.3. Parameter Requirements ....................................10
      4.4. Canonicalization and Format Requirements ..................10
      4.5. Interchange Recommendations ...............................11
      4.6. Security Requirements .....................................11
      4.7. Requirements specific to XML media types ..................13
      4.8. Encoding Requirements .....................................13
      4.9. Usage and Implementation Non-requirements .................13
      4.10. Publication Requirements .................................14
      4.11. Additional Information ...................................15
   5. Registration Procedure .........................................15
      5.1. Preliminary Community Review ..............................16
      5.2. IESG Approval .............................................16
      5.3. IANA Registration .........................................16
      5.4. Media Types Reviewer ......................................16
   6. Comments on Media Type Registrations ...........................17
   7. Location of Registered Media Type List .........................17
   8. IANA Procedures for Registering Media Types ....................17
   9. Change Procedures ..............................................18
   10. Registration Template .........................................19
   11. Security Considerations .......................................20
   12. IANA Considerations ...........................................20
   13. Acknowledgements ..............................................20
   14. References ....................................................20
   Appendix A.  Grandfathered Media Types ............................22
   Appendix B.  Changes Since RFC 2048 ...............................22

1.  Introduction

   Recent Internet protocols have been carefully designed to be easily
   extensible in certain areas.  In particular, many protocols,
   including but not limited to MIME [RFC2045], are capable of carrying
   arbitrary labeled content.  A mechanism is needed to label such
   content and a registration process is needed for these labels, to
   ensure that the set of such values is developed in an orderly, well-
   specified, and public manner.

   This document defines media type specification and registration
   procedures that use the Internet Assigned Numbers Authority (IANA) as
   a central registry.

   Historical Note

      The media type registration process was initially defined for
      registering media types for use in the context of the asynchronous
      Internet mail environment.  In this mail environment there is a
      need to limit the number of possible media types, to increase the
      likelihood of interoperability when the capabilities of the remote
      mail system are not known.  As media types are used in new
      environments in which the proliferation of media types is not a
      hindrance to interoperability, the original procedure proved
      excessively restrictive and had to be generalized.  This was
      initially done in [RFC2048], but the procedure defined there was
      still part of the MIME document set.  The media type specification
      and registration procedure has now been moved to this separate
      document, to make it clear that it is independent of MIME.

      It may be desirable to restrict the use of media types to specific
      environments or to prohibit their use in other environments.  This
      revision attempts for the first time to incorporate such
      restrictions into media type registrations in a systematic way.
      See Section 4.9 for additional discussion.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   This specification makes use of the Augmented Backus-Naur Form (ABNF)
   [RFC4234] notation, including the core rules defined in Appendix A of
   that document.

2.  Media Type Registration Preliminaries

   Registration of a new media type or types starts with the
   construction of a registration proposal.  Registration may occur
   within several different registration trees that have different
   requirements, as discussed below.  In general, a new registration
   proposal is circulated and reviewed in a fashion appropriate to the
   tree involved.  The media type 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.  Registration Trees and Subtype Names

   In order to increase the efficiency and flexibility of the
   registration process, different structures of subtype names may be
   registered to accommodate the different natural requirements for,
   e.g., a subtype that will be recommended for wide support and
   implementation by the Internet community, or a subtype that is used
   to move files associated with proprietary software.  The following
   subsections define registration "trees" that are distinguished by the
   use of faceted names, e.g., names of the form
   "tree.subtree...subtype".  Note that some media types defined prior
   to this document do not conform to the naming conventions described
   below.  See Appendix A for a discussion of them.

3.1.  Standards Tree

   The standards tree is intended for types of general interest to the
   Internet community.  Registrations in the standards tree MUST be
   approved by the IESG and MUST correspond to a formal publication by a
   recognized standards body.  In the case of registration for the IETF
   itself, the registration proposal MUST be published as an RFC.
   Standards-tree registration RFCs can either be standalone
   "registration only" RFCs, or they can be incorporated into a more
   general specification of some sort.

   Media types in the standards tree are normally denoted by names that
   are not explicitly faceted, i.e., do not contain period (".", full
   stop) characters.

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

3.2.  Vendor Tree

   The vendor tree is used for media types associated with commercially
   available products.  "Vendor" or "producer" are construed as
   equivalent and very broadly in this context.

   A registration may be placed in the vendor tree by anyone who needs
   to interchange files associated with the particular product.
   However, the registration formally belongs to the vendor or
   organization producing the software or file format being registered.
   Changes to the specification will be made at their request, as
   discussed in subsequent sections.

   Registrations in the vendor tree will be distinguished by the leading
   facet "vnd.".  That may be followed, at the discretion of the
   registrant, by either a media subtype name from a well-known producer
   (e.g., "vnd.mudpie") or by an IANA-approved designation of the
   producer's name that is followed by a media type or product
   designation (e.g., vnd.bigcompany.funnypictures).

   While public exposure and review of media types to be registered in
   the vendor tree is not required, using the ietf-types@iana.org
   mailing list for review is strongly encouraged to improve the quality
   of those specifications.  Registrations in the vendor tree may be
   submitted directly to the IANA.

3.3.  Personal or Vanity Tree

   Registrations for media types created experimentally or as part of
   products that are not distributed commercially may be registered in
   the personal or vanity tree.  The registrations are distinguished by
   the leading facet "prs.".

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

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

3.4.  Special x. Tree

   For convenience and symmetry with this registration scheme, subtype
   names with "x." as the first facet may be used for the same purposes
   for which names starting in "x-" are used.  These types are

   unregistered, experimental, and for use 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 types.  Therefore, use of
   both "x-" and "x." forms is discouraged.

   Types in this tree MUST NOT be registered.

3.5.  Additional Registration Trees

   From time to time and as required by the community, the IANA may, by
   and 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; for example, scientific societies may register
   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 registrations in
   the standards tree.  Establishment of these new trees will be
   announced through RFC publication approved by the IESG.

4.  Registration Requirements

   Media type 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.

4.1.  Functionality Requirement

   Media types MUST function as an actual media format.  Registration of
   things that are better thought of as a transfer encoding, as a
   charset, or as a collection of separate entities of another type, is
   not allowed.  For example, although applications exist to decode the
   base64 transfer encoding [RFC2045], base64 cannot be registered as a
   media type.

   This requirement applies regardless of the registration tree
   involved.

4.2.  Naming Requirements

   All registered media types MUST be assigned type and subtype names.
   The combination of these names serves to uniquely identify the media
   type, and the format of the subtype name identifies the registration
   tree.  Both type and subtype names are case-insensitive.

   Type and subtype names beginning with "X-" are reserved for
   experimental use and MUST NOT be registered.  This parallels the
   restriction on the x. tree, as discussed in Section 3.4.

   Type and subtype names MUST conform to the following ABNF:

       type-name = reg-name
       subtype-name = reg-name

       reg-name = 1*127reg-name-chars
       reg-name-chars = ALPHA / DIGIT / "!" /
                       "#" / "$" / "&" / "." /
                       "+" / "-" / "^" / "_"

   Note that this syntax is somewhat more restrictive than what is
   allowed by the ABNF in [RFC2045].

   In accordance with the rules specified in [RFC3023], media subtypes
   that do not represent XML entities MUST NOT be given a name that ends
   with the "+xml" suffix.  More generally, "+suffix" constructs should
   be used with care, given the possibility of conflicts with future
   suffix definitions.

   While it is possible for a given media type to be assigned additional
   names, the use of different names to identify the same media type is
   discouraged.

   These requirements apply regardless of the registration tree
   involved.

   The choice of top-level type name MUST take into account the nature
   of media type involved.  New subtypes of top-level types MUST conform
   to the restrictions of the top-level type, if any.  The following
   sections describe each of the initial set of top-level types and
   their associated restrictions.  Additionally, various protocols,
   including but not limited to MIME, MAY impose additional restrictions
   on the media types they can transport.  (See [RFC2046] for additional
   information on the restrictions MIME imposes.)

4.2.1.  Text Media Types

   The "text" media type is intended for sending material that is
   principally textual in form.  A "charset" parameter MAY be used to
   indicate the charset of the body text for "text" subtypes, notably
   including the subtype "text/plain", which is a generic subtype for
   plain text defined in [RFC2046].  If defined, a text "charset"

   parameter MUST be used to specify a charset name defined in
   accordance to the procedures laid out in [RFC2978].

   Plain text does not provide for or allow formatting commands, font
   attribute specifications, processing instructions, interpretation
   directives, or content markup.  Plain text is seen simply as a linear

   sequence of characters, possibly interrupted by line breaks or page
   breaks.  Plain text MAY allow the stacking of several characters in
   the same position in the text.  Plain text in scripts like Arabic and
   Hebrew may also include facilities that allow the arbitrary mixing of
   text segments with opposite writing directions.

   Beyond plain text, there are many formats for representing what might
   be known as "rich text".  An interesting characteristic of many such
   representations is that they are to some extent readable even without
   the software that interprets them.  It is useful to distinguish them,
   at the highest level, from such unreadable data as images, audio, or
   text represented in an unreadable form.  In the absence of
   appropriate interpretation software, it is reasonable to present
   subtypes of "text" to the user, while it is not reasonable to do so
   with most non-textual data.  Such formatted textual data should be
   represented using subtypes of "text".

4.2.2.  Image Media Types

   A media type of "image" indicates that the content specifies or more
   separate images that require appropriate hardware to display.  The
   subtype names the specific image format.

4.2.3.  Audio Media Types

   A media type of "audio" indicates that the content contains audio
   data.

4.2.4.  Video Media Types

   A media type of "video" indicates that the content specifies a time-
   varying-picture image, possibly with color and coordinated sound.
   The term 'video' is used in its most generic sense, rather than with
   reference to any particular technology or format, and is not meant to
   preclude subtypes such as animated drawings encoded compactly.

   Note that although in general this document strongly discourages the
   mixing of multiple media in a single body, it is recognized that many
   so-called video formats include a representation for synchronized
   audio and/or text, and this is explicitly permitted for subtypes of
   "video".

4.2.5.  Application Media Types

   The "application" media type is to be used for discrete data that do
   not fit in any of the media types, and particularly for data to be
   processed by some type of application program.  This is information
   that must be processed by an application before it is viewable or
   usable by a user.  Expected uses for the "application" media type
   include but are not limited to file transfer, spreadsheets,
   presentations, scheduling data, and languages for "active"
   (computational) material.  (The latter, in particular, can pose
   security problems that must be understood by implementors, and are
   considered in detail in the discussion of the "application/
   PostScript" media type in [RFC2046].)

   For example, a meeting scheduler might define a standard
   representation for information about proposed meeting dates.  An
   intelligent user agent would use this information to conduct a dialog
   with the user, and might then send additional material based on that
   dialog.  More generally, there have been several "active" languages
   developed in which programs in a suitably specialized language are
   transported to a remote location and automatically run in the
   recipient's environment.  Such applications may be defined as
   subtypes of the "application" media type.

   The subtype of "application" will often be either the name or include
   part of the name of the application for which the data are intended.
   This does not mean, however, that any application program name may be
   used freely as a subtype of "application".

4.2.6.  Multipart and Message Media Types

   Multipart and message are composite types, that is, they provide a
   means of encapsulating zero or more objects, each labeled with its
   own media type.

   All subtypes of multipart and message MUST conform to the syntax
   rules and other requirements specified in [RFC2046].

4.2.7.  Additional Top-level Types

   In some cases a new media type may not "fit" under any currently
   defined top-level content type.  Such cases are expected to be quite
   rare.  However, if such a case does arise a new top-level type can be
   defined to accommodate it.  Such a definition MUST be done via
   standards-track RFC; no other mechanism can be used to define
   additional top-level content types.

4.3.  Parameter Requirements

   Media types MAY elect to use one or more media type parameters, or
   some parameters may be automatically made available to the media type
   by virtue of being a subtype of a content type that defines a set of
   parameters applicable to any of its subtypes.  In either case, the
   names, values, and meanings of any parameters MUST be fully specified

   when a media type is registered in the standards tree, and SHOULD be
   specified as completely as possible when media types are registered
   in the vendor or personal trees.

   Parameter names have the syntax as media type names and values:

       parameter-name = reg-name

   Note that this syntax is somewhat more restrictive than what is
   allowed by the ABNF in [RFC2045] and amended by [RFC2231].

   There is no defined syntax for parameter values.  Therefore
   registrations MUST specify parameter value syntax.  Additionally,
   some transports impose restrictions on parameter value syntax, so
   care should be taken to limit the use of potentially problematic
   syntaxes; e.g., pure binary valued parameters, while permitted in
   some protocols, probably should be avoided.

   New parameters SHOULD NOT be defined as a way to introduce new
   functionality in types registered in the standards tree, although new
   parameters MAY be added to convey additional information that does
   not otherwise change existing functionality.  An example of this
   would be a "revision" parameter to indicate a revision level of an
   external specification such as JPEG.  Similar behavior is encouraged
   for media types registered in the vendor or personal trees but is not
   required.

4.4.  Canonicalization and Format Requirements

   All registered media types MUST employ a single, canonical data
   format, regardless of registration tree.

   A precise and openly available specification of the format of each
   media type MUST exist for all types registered in the standards tree
   and MUST at a minimum be referenced by, if it isn't actually included
   in, the media type registration proposal itself.

   The specifications of format and processing particulars may or may
   not be publicly available for media types registered in the vendor
   tree, and such registration proposals are explicitly permitted to

   limit specification to which software and version produce or process
   such media types.  References to or inclusion of format
   specifications in registration proposals is encouraged but not
   required.

   Format specifications are still required for registration in the
   personal tree, but may be either published as RFCs or otherwise
   deposited with the IANA.  The deposited specifications will meet the
   same criteria as those required to register a well-known TCP port
   and, in particular, need not be made public.

   Some media types involve the use of patented technology.  The
   registration of media types involving patented technology is
   specifically permitted.  However, the restrictions set forth in
   [RFC2026] on the use of patented technology in IETF standards-track
   protocols must be respected when the specification of a media type is
   part of a standards-track protocol.  In addition, other standards
   bodies making use of the standards tree may have their own rules
   regarding intellectual property that must be observed in their
   registrations.

4.5.  Interchange Recommendations

   Media types SHOULD interoperate across as many systems and
   applications as possible.  However, some media types will inevitably
   have problems interoperating across different platforms.  Problems
   with different versions, byte ordering, and specifics of gateway
   handling can and will arise.

   Universal interoperability of media types is not required, but known
   interoperability issues SHOULD be identified whenever possible.
   Publication of a media type 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.

4.6.  Security Requirements

   An analysis of security issues MUST be done for all types registered
   in the standards Tree.  A similar analysis for media types registered
   in the vendor or personal trees is encouraged but not required.
   However, regardless of what security analysis has or has not been
   done, 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 this type" MUST

   NOT be confused with "the security issues associates with this type
   have not been assessed".

   There is absolutely no requirement that media types registered in any
   tree be secure or completely free from risks.  Nevertheless, all
   known security risks MUST be identified in the registration of a
   media type, 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 media types" mechanism described
   in Section 6 below.

   Some of the issues that should be looked at in a security analysis of
   a media type are:

   o  Complex media types may include provisions for directives that
      institute actions on a recipient's files or other resources.  In
      many cases provision is made for originators to specify arbitrary
      actions in an unrestricted fashion that may then have devastating
      effects.  See the registration of the application/postscript media
      type in [RFC2046] for an example of such directives and how they
      should be described in a media type registration.

   o  All registrations MUST state whether or not they employ such
      "active content", and if they do, they MUST state what steps have
      been taken to protect users of the media type from harm.

   o  Complex media types may include provisions for directives that
      institute actions that, while not directly harmful to the
      recipient, may result in disclosure of information that either
      facilitates a subsequent attack or else violates a recipient's
      privacy in some way.  Again, the registration of the
      application/postscript media type illustrates how such directives
      can be handled.

   o  A media type that employs compression may provide an opportunity
      for sending a small amount of data that, when received and
      evaluated, expands enormously to consume all of the recipient's
      resources.  All media types SHOULD state whether or not they
      employ compression, and if they do they should discuss what steps
      need to be taken to avoid such attacks.

   o  A media type might be targeted for applications that require some
      sort of security assurance but not provide the necessary security
      mechanisms themselves.  For example, a media type could be defined
      for storage of confidential medical information that in turn

      requires an external confidentiality service, or which is designed
      for use only within a secure environment.

4.7.  Requirements specific to XML media types

   There are a number of additional requirements specific to the
   registration of XML media types.  These requirements are specified in
   [RFC3023].

4.8.  Encoding Requirements

   Some transports impose restrictions on the type of data they can
   carry.  For example, Internet mail traditionally was limited to 7bit
   US-ASCII text.  Encoding schemes are often used to work around such
   transport limitations.

   It is therefore useful to note what sort of data a media type can
   consist of as part of its registration.  An "encoding considerations"
   field is provided for this purpose.  Possible values of this field
   are:

   7bit: The content of the media type consists solely of CRLF-delimited
      7bit US-ASCII text.

   8bit: The content of the media type consists solely of CRLF-delimited
      8bit text.

   binary: The content consists of unrestricted sequence of octets.

   framed: The content consists of a series of frames or packets without
      internal framing or alignment indicators.  Additional out-of-band
      information is needed to interpret the data properly, including
      but not necessarily limited to, knowledge of the boundaries
      between successive frames and knowledge of the transport
      mechanism.  Note that media types of this sort cannot simply be
      stored in a file or transported as a simple stream of octets;
      therefore, such media types are unsuitable for use in many
      traditional protocols.  A commonly used transport with framed
      encoding is the Real-time Transport Protocol, RTP.  Additional
      rules for framed encodings defined for transport using RTP are
      given in [RFC3555].

   Additional restrictions on 7bit and 8bit text are given in [RFC2046].

4.9.  Usage and Implementation Non-requirements

   In the asynchronous mail environment, where information on the
   capabilities of the remote mail agent is frequently not available to

   the sender, maximum interoperability is attained by restricting the
   media types used to those "common" formats expected to be widely
   implemented.  This was asserted in the past as a reason to limit the
   number of possible media types, and it resulted in a registration
   process with a significant hurdle and delay for those registering
   media types.

   However, the need for "common" media types does not require limiting
   the registration of new media types.  If a limited set of media types
   is recommended for a particular application, that should be asserted
   by a separate applicability statement specific for the application
   and/or environment.

   Therefore, universal support and implementation of a media type is
   NOT a requirement for registration.  However, if a media type is
   explicitly intended for limited use, this MUST be noted in its
   registration.  The "Restrictions on Usage" field is provided for this
   purpose.

4.10.  Publication Requirements

   Proposals for media types registered in the standards tree by the
   IETF itself MUST be published as RFCs.  RFC publication of vendor and
   personal media type proposals is encouraged but not required.  In all
   cases the IANA will retain copies of all media type proposals and
   "publish" them as part of the media types registration tree itself.

   As stated previously, standards tree registrations for media types
   defined in documents produced by other standards bodies MUST be
   described by a formal standards specification produced by that body.
   Such specifications MUST contain an appropriate media type
   registration template taken from Section 10.  Additionally, the
   copyright on the registration template MUST allow the IANA to copy it
   into the IANA registry.

   Other than IETF registrations in the standards tree, the registration
   of a data type does not imply endorsement, approval, or
   recommendation by the IANA or the IETF or even certification that the
   specification is adequate.  To become Internet Standards, a protocol
   or data object must go through the IETF standards process.  This is
   too difficult and too lengthy a process for the convenient
   registration of media types.

   The standards tree exists for media types that do require a
   substantive review and approval process in a recognized standards
   body.  The vendor and personal trees exist for those media types that
   do not require such a process.  It is expected that applicability
   statements for particular applications will be published from time to

   time in the IETF, recommending implementation of, and support for,
   media types that have proven particularly useful in those contexts.

   As discussed above, registration of a top-level type requires
   standards-track processing in the IETF and, hence, RFC publication.

4.11.  Additional Information

   Various sorts of optional information SHOULD be included in the
   specification of a media type if it is available:

   o  Magic number(s) (length, octet values).  Magic numbers are byte
      sequences that are always present at a given place in the file and
      thus can be used to identify entities as being of a given media
      type.

   o  File name extension(s) commonly used on one or more platforms to
      indicate that some file contains a given media type.

   o  Mac OS File Type code(s) (4 octets) used to label files containing
      a given media type.

   o  Information about how fragment/anchor identifiers [RFC3986] are
      constructed for use in conjunction with this media type.

   In the case of a registration in the standards tree, this additional
   information MAY be provided in the formal specification of the media
   type.  It is suggested that this be done by incorporating the IANA
   media type registration form into the specification itself.

5.  Registration Procedure

   The media type registration procedure is not a formal standards
   process, but rather an administrative procedure intended to allow
   community comment and sanity checking without excessive time delay.

   The normal IETF processes should be followed for all IETF
   registrations in the standards tree.  The posting of an Internet
   Draft is a necessary first step, followed by posting to the
   ietf-types@iana.org list as discussed below.

   Registrations in the vendor and personal tree should be submitted
   directly to the IANA, ideally after first posting to the
   ietf-types@iana.org list for review.

   Proposed registrations in the standards tree by other standards
   bodies should be communicated to the IESG (at iesg@ietf.org) and to
   the ietf-types list (at ietf-types@iana.org).  Prior posting as an

   Internet Draft is not required for these registrations, but may be
   helpful to the IESG and is encouraged.

5.1.  Preliminary Community Review

   Notice of a potential media type registration in the standards tree
   MUST be sent to the "ietf-types@iana.org" mailing list for review.
   This mailing list has been established for the purpose of reviewing
   proposed media and access types.  Registrations in other trees MAY be
   sent to the list for review as well.

   The intent of the public posting to this list is to solicit comments
   and feedback on the choice of type/subtype name, the unambiguity of
   the references with respect to versions and external profiling
   information, and a review of any interoperability or security
   considerations.  The submitter may submit a revised registration or
   abandon the registration completely and at any time.

5.2.  IESG Approval

   Media types registered in the standards tree MUST be approved by the
   IESG prior to registration.

5.3.  IANA Registration

   Provided that the media type meets all of the relevant requirements
   and has obtained whatever approval is necessary, the author may
   submit the registration request to the IANA.  Registration requests
   can be sent to iana@iana.org.  A web form for registration requests
   is also available:

     http://www.iana.org/cgi-bin/mediatypes.pl

   Sending to ietf-types@iana.org does not constitute submitting the
   registration to the IANA.

   When the registration is either part of an RFC publication request or
   a registration in the standards tree submitted to the IESG, close
   coordination between the IANA and the IESG means IESG approval in
   effect submits the registration to the IANA.  There is no need for an
   additional registration request in such cases.

5.4.  Media Types Reviewer

   Registrations submitted to the IANA will be passed on to the media
   types reviewer.  The media types reviewer, who is appointed by the
   IETF Applications Area Director(s), will review the registration to
   make sure it meets the requirements set forth in this document.

   Registrations that do not meet these requirements will be returned to
   the submitter for revision.

   Decisions made by the media types reviewer may be appealed to the
   IESG using the procedure specified in [RFC2026] section 6.5.4.

   Once a media type registration has passed review, the IANA will
   register the media type and make the media type registration
   available to the community.

6.  Comments on Media Type Registrations

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

7.  Location of Registered Media Type List

   Media type registrations are listed by the IANA at:

      http://www.iana.org/assignments/media-types/

8.  IANA Procedures for Registering Media Types

   The IANA will only register media types in the standards tree in
   response to a communication from the IESG stating that a given
   registration has been approved.  Vendor and personal types will be
   registered by the IANA automatically and without any formal approval
   process as long as the following minimal conditions are met:

   o  Media types MUST function as an actual media format.  In
      particular, charsets and transfer encodings MUST NOT be registered
      as media types.

   o  All media types MUST have properly formed type and subtype names.
      All type names MUST be defined by a standards-track RFC.  All
      type/subtype name pairs MUST be unique and MUST contain the proper
      tree prefix.

   o  Types registered in the personal tree MUST either provide a format
      specification or a pointer to one.

   o  All media types MUST have a reasonable security considerations
      section.  (It is neither possible nor necessary for the IANA to
      conduct a comprehensive security review of media type
      registrations.  Nevertheless, the IANA has the authority to
      identify obviously incompetent material and return it to the
      submitter for revision.)

   Registrations in the standards tree MUST satisfy the additional
   requirement that they originate from the IETF itself or from another
   standards body recognized as such by the IETF.

9.  Change Procedures

   Once a media type 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 same procedure that would be appropriate
   for the original registration request is used to process a change
   request.

   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 entities that were valid
   under the previous definition invalid under the new definition.

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

   The IESG may reassign responsibility for a media type.  The most
   common case of this will be to enable changes to be made to types
   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.

   Media type registrations may not be deleted; media types that are no
   longer believed appropriate for use can be declared OBSOLETE by a
   change to their "intended use" field; such media types will be
   clearly marked in the lists published by the IANA.

10.  Registration Template

   To: ietf-types@iana.org
   Subject: Registration of media type XXX/YYY

   Type name:

   Subtype name:

   Required parameters:

   Optional parameters:

   Encoding considerations:

   Security considerations:

   Interoperability considerations:

   Published specification:

   Applications that use this media type:

   Additional information:

     Magic number(s):
     File extension(s):
     Macintosh file type code(s):

   Person & email address to contact for further information:

   Intended usage:

   (One of COMMON, LIMITED USE or OBSOLETE.)

   Restrictions on usage:

   (Any restrictions on where the media type can be used go here.)

   Author:

   Change controller:

   (Any other information that the author deems interesting may be added
   below this line.)

   Some discussion of Macintosh file type codes and their purpose can be
   found in [MacOSFileTypes].  Additionally, please refrain from writing

   "none" or anything similar when no file extension or Macintosh file
   type is specified, lest "none" be confused with an actual code value.

11.  Security Considerations

   Security requirements for media type registrations are discussed in
   Section 4.6.

12.  IANA Considerations

   The purpose of this document is to define IANA registries for media
   types.

13.  Acknowledgements

   The current authors would like to acknowledge their debt to the late
   Dr. Jon Postel, whose general model of IANA registration procedures
   and specific contributions shaped the predecessors of this document
   [RFC2048].  We hope that the current version is one with which he
   would have agreed but, as it is impossible to verify that agreement,
   we have regretfully removed his name as a co-author.

14.  References

14.1.  Normative References

   [RFC2045]        Freed, N. and N. Borenstein, "Multipurpose Internet
                    Mail Extensions (MIME) Part One: Format of Internet
                    Message Bodies", RFC 2045, November 1996.

   [RFC2046]        Freed, N. and N. Borenstein, "Multipurpose Internet
                    Mail Extensions (MIME) Part Two: Media Types", RFC
                    2046, November 1996.

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

   [RFC2978]        Freed, N. and J. Postel, "IANA Charset Registration
                    Procedures", BCP 19, RFC 2978, October 2000.

   [RFC3023]        Murata, M., St. Laurent, S., and D. Kohn, "XML Media
                    Types", RFC 3023, January 2001.

   [RFC3555]        Casner, S. and P. Hoschka, "MIME Type Registration
                    of RTP Payload Formats", RFC 3555, July 2003.

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

   [RFC4234]        Crocker, D. Ed., and P. Overell, "Augmented BNF for
                    Syntax Specifications: ABNF", RFC 4234, October
                    2005.

14.2.  Informative References

   [MacOSFileTypes] Apple Computer, Inc., "Mac OS: File Type and Creator
                    Codes, and File Formats", Apple Knowledge Base
                    Article 55381, June 1993,
                    <http://www.info.apple.com/kbnum/n55381>.

   [RFC2026]        Bradner, S., "The Internet Standards Process --
                    Revision 3", BCP 9, RFC 2026, October 1996.

   [RFC2048]        Freed, N., Klensin, J., and J. Postel, "Multipurpose
                    Internet Mail Extensions (MIME) Part Four:
                    Registration Procedures", BCP 13, RFC 2048, November
                    1996.

   [RFC2231]        Freed, N. and K. Moore, "MIME Parameter Value and
                    Encoded Word Extensions: Character Sets, Languages,
                    and Continuations", RFC 2231, November 1997.

Appendix A.  Grandfathered Media Types

   A number of media types, registered prior to 1996, would, if
   registered under the guidelines in this document, be placed into
   either the vendor or personal trees.  Reregistration of those types
   to reflect the appropriate trees is encouraged but not required.
   Ownership and change control principles outlined in this document
   apply to those types as if they had been registered in the trees
   described above.

Appendix B.  Changes Since RFC 2048

   o  Media type specification and registration procedures have been
      moved out of the MIME document set to this separate specification.

   o  The various URLs and addresses in this document have been changed
      so they all refer to iana.org rather than isi.edu.  Additionally,
      many of the URLs have been changed to use HTTP; formerly they used
      FTP.

   o  Much of the document has been clarified in the light of
      operational experience with these procedures.

   o  The unfaceted IETF tree is now called the standards tree, and the
      registration rules for this tree have been relaxed to allow use by
      other standards bodies.

   o  The text describing the media type registration procedure has
      clarified.

   o  The rules and requirements for constructing security
      considerations sections have been extended and clarified.

   o  RFC 3023 is now referenced as the source of additional information
      concerning the registration of XML media types.

   o  Several of the references in this document have been updated to
      refer to current versions of the relevant specifications.

   o  A note has been added discouraging the assignment of multiple
      names to a single media type.

   o  Security considerations and IANA considerations sections have been
      added.

   o  Concerns regarding copyrights on media type registration templates
      produced by other standards bodies have been dealt with by
      requiring that the IANA be allowed to copy the registration
      template into the registry.

   o  The basic registration requirements for the various top-level
      types have been moved from RFC 2046 to this document.

   o  A syntax is now specified for media type, subtype, and parameter
      names.

   o  Imposed a maximum length of 127 on all media type and subtype
      names.

   o  A note has been added to caution against excessive use of
      "+suffix" constructs in subtype names.

   o  The encoding considerations field has been extended to allow the
      value "framed".

   o  A reference describing Macintosh Type codes has been added.

   o  Ietf-types list review of registrations in the standards tree is
      now required rather than just recommended.

Authors' Addresses

   Ned Freed
   Sun Microsystems
   3401 Centrelake Drive, Suite 410
   Ontario, CA  92761-1205
   USA

   Phone: +1 909 457 4293
   EMail: ned.freed@mrochek.com

   John C. Klensin
   1770 Massachusetts Ave, #322
   Cambridge, MA  02140

   EMail: klensin+ietf@jck.com

Full Copyright Statement

   Copyright (C) The Internet Society (2005).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.

Freed & Klensin          Best Current Practice                 [Page 24]

========================================================================

Network Working Group                                           N. Freed
Request for Comments: 4289                              Sun Microsystems
BCP: 13                                                       J. Klensin
Obsoletes: 2048                                            December 2005
Category: Best Current Practice

        Multipurpose Internet Mail Extensions (MIME) Part Four:
                        Registration Procedures

Status of This Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document specifies IANA registration procedures for MIME
   external body access types and content-transfer-encodings.

Table of Contents

   1. Introduction ....................................................2
   2. External Body Access Types ......................................3
      2.1. Registration Requirements ..................................3
         2.1.1. Naming Requirements ...................................3
         2.1.2. Mechanism Specification Requirements ..................3
         2.1.3. Publication Requirements ..............................4
         2.1.4. Security Requirements .................................4
      2.2. Registration Procedure .....................................4
         2.2.1. Present the Access Type to the Community ..............4
         2.2.2. Access Type Reviewer ..................................4
         2.2.3. IANA Registration .....................................5
      2.3. Location of Registered Access Type List ....................5
      2.4. IANA Procedures for Registering Access Types ...............5
   3. Transfer Encodings ..............................................5
      3.1. Transfer Encoding Requirements .............................6
         3.1.1. Naming Requirements ...................................6
         3.1.2. Algorithm Specification Requirements ..................6
         3.1.3. Input Domain Requirements .............................6
         3.1.4. Output Range Requirements .............................6
         3.1.5. Data Integrity and Generality Requirements ............7
         3.1.6. New Functionality Requirements ........................7
         3.1.7. Security Requirements .................................7
      3.2. Transfer Encoding Definition Procedure .....................7
      3.3. IANA Procedures for Transfer Encoding Registration .........8
      3.4. Location of Registered Transfer Encodings List .............8
   4. Security Considerations .........................................8
   5. IANA Considerations .............................................8
   6. Acknowledgements ................................................8
   7. References ......................................................9
   A.  Changes Since RFC 2048 .........................................9

1.  Introduction

   Recent Internet protocols have been carefully designed to be easily
   extensible in certain areas.  In particular, MIME [RFC2045] is an
   open-ended framework and can accommodate additional object types,
   charsets, and access methods without any changes to the basic
   protocol.  A registration process is needed, however, to ensure that
   the set of such values is developed in an orderly, well-specified,
   and public manner.

   This document defines registration procedures that use the Internet
   Assigned Numbers Authority (IANA) as a central registry for these
   values.

   Note:

      Registration of media types and charsets for use in MIME are
      specified in separate documents [RFC4288] [RFC2278] and are not
      addressed here.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  External Body Access Types

   [RFC2046] defines the message/external-body media type, whereby a
   MIME entity can act as pointer to the actual body data in lieu of
   including the data directly in the entity body.  Each
   message/external-body reference specifies an access type, which
   determines the mechanism used to retrieve the actual body data.  RFC
   2046 defines an initial set of access types but allows for the
   registration of additional access types to accommodate new retrieval
   mechanisms.

2.1.  Registration Requirements

   New access type specifications MUST conform to the requirements
   described below.

2.1.1.  Naming Requirements

   Each access type MUST have a unique name.  This name appears in the
   access-type parameter in the message/external-body content-type
   header field and MUST conform to MIME content type parameter syntax.

2.1.2.  Mechanism Specification Requirements

   All of the protocols, transports, and procedures used by a given
   access type MUST be described, either in the specification of the
   access type itself or in some other publicly available specification,
   in sufficient detail for the access type to be implemented by any
   competent implementor.  Use of secret and/or proprietary methods in
   access types is expressly prohibited.  The restrictions imposed by
   [RFC2026] on the standardization of patented algorithms must be
   respected as well.

2.1.3.  Publication Requirements

   All access types MUST be described by an RFC.  The RFC may be
   informational rather than standards-track, although standards-track
   review and approval are encouraged for all access types.

2.1.4.  Security Requirements

   Any known security issues that arise from the use of the access type
   MUST be completely and fully described.  It is not required that the
   access type be secure or that it be free from risks, but it is
   required that the known risks be identified.  Publication of a new
   access type does not require an exhaustive security review, and the
   security considerations section is subject to continuing evaluation.
   Additional security considerations SHOULD be addressed by publishing
   revised versions of the access type specification.

2.2.  Registration Procedure

   Registration of a new access type starts with the publication of the
   specification as an Internet Draft.

2.2.1.  Present the Access Type to the Community

   A proposed access type specification is sent to the
   "ietf-types@iana.org" mailing list for a two-week review period.
   This mailing list has been established for the purpose of reviewing
   proposed access and media types.  Proposed access types are not
   formally registered and must not be used.

   The intent of the public posting is to solicit comments and feedback
   on the access type specification and a review of any security
   considerations.

2.2.2.  Access Type Reviewer

   When the two-week period has passed, the access type reviewer, who is
   appointed by the IETF Applications Area Director(s), either forwards
   the request to iana@iana.org or rejects it because of significant
   objections raised on the list.

   Decisions made by the reviewer must be posted to the ietf-types
   mailing list within 14 days.  Decisions made by the reviewer may be
   appealed to the IESG as specified in [RFC2026].

2.2.3.  IANA Registration

   Provided that the access type either has passed review or has been
   successfully appealed to the IESG, the IANA will register the access
   type and make the registration available to the community.  The
   specification of the access type must also be published as an RFC.

2.3.  Location of Registered Access Type List

   Access type registrations are listed by the IANA on the following web
   page:

     http://www.iana.org/assignments/access-types

2.4.  IANA Procedures for Registering Access Types

   The identity of the access type reviewer is communicated to the IANA
   by the IESG.  The IANA then only acts either in response to access
   type definitions that are approved by the access type reviewer and
   forwarded to the IANA for registration, or in response to a
   communication from the IESG that an access type definition appeal has
   overturned the access type reviewer's ruling.

3.  Transfer Encodings

   Transfer encodings are transformations applied to MIME media types
   after conversion to the media type's canonical form.  Transfer
   encodings are used for several purposes:

   o  Many transports, especially message transports, can only handle
      data consisting of relatively short lines of text.  There can be
      severe restrictions on what characters can be used in these lines
      of text.  Some transports are restricted to a small subset of US-
      ASCII, and others cannot handle certain character sequences.
      Transfer encodings are used to transform binary data into a
      textual form that can survive such transports.  Examples of this
      sort of transfer encoding include the base64 and quoted-printable
      transfer encodings defined in [RFC2045].

   o  Image, audio, video, and even application entities are sometimes
      quite large.  Compression algorithms are often effective in
      reducing the size of large entities.  Transfer encodings can be
      used to apply general-purpose non-lossy compression algorithms to
      MIME entities.

   o  Transport encodings can be defined as a means of representing
      existing encoding formats in a MIME context.

   IMPORTANT:  The standardization of a large number of different
   transfer encodings is seen as a significant barrier to widespread
   interoperability and is expressly discouraged.  Nevertheless, the
   following procedure has been defined in order to provide a means of
   defining additional transfer encodings, should standardization
   actually be justified.

3.1.  Transfer Encoding Requirements

   Transfer encoding specifications MUST conform to the requirements
   described below.

3.1.1.  Naming Requirements

   Each transfer encoding MUST have a unique name.  This name appears in
   the Content-Transfer-Encoding header field and MUST conform to the
   syntax of that field.

3.1.2.  Algorithm Specification Requirements

   All of the algorithms used in a transfer encoding (e.g., conversion
   to printable form, compression) MUST be described in their entirety
   in the transfer encoding specification.  Use of secret and/or

   proprietary algorithms in standardized transfer encodings is
   expressly prohibited.  The restrictions imposed by [RFC2026] on the
   standardization of patented algorithms MUST be respected as well.

3.1.3.  Input Domain Requirements

   All transfer encodings MUST be applicable to an arbitrary sequence of
   octets of any length.  Dependence on particular input forms is not
   allowed.

   It should be noted that the 7bit and 8bit encodings do not conform to
   this requirement.  Aside from the undesirability of having
   specialized encodings, the intent here is to forbid the addition of
   additional encodings similar to, or redundant with, 7bit and 8bit.

3.1.4.  Output Range Requirements

   There is no requirement that a particular transfer encoding produce a
   particular form of encoded output.  However, the output format for
   each transfer encoding MUST be fully and completely documented.  In
   particular, each specification MUST clearly state whether the output
   format always lies within the confines of 7bit or 8bit or is simply
   pure binary data.

3.1.5.  Data Integrity and Generality Requirements

   All transfer encodings MUST be fully invertible on any platform; it
   MUST be possible for anyone to recover the original data by
   performing the corresponding decoding operation.  Note that this
   requirement effectively excludes all forms of lossy compression as
   well as all forms of encryption from use as a transfer encoding.

3.1.6.  New Functionality Requirements

   All transfer encodings MUST provide some sort of new functionality.
   Some degree of functionality overlap with previously defined transfer
   encodings is acceptable, but any new transfer encoding MUST also
   offer something no other transfer encoding provides.

3.1.7.  Security Requirements

   To the greatest extent possible, transfer encodings SHOULD NOT
   contain known security issues.  Regardless, any known security issues
   that arise from the use of the transfer encoding MUST be completely
   and fully described.  If additional security issues come to light
   after initial publication and registration, they SHOULD be addressed
   by publishing revised versions of the transfer encoding
   specification.

3.2.  Transfer Encoding Definition Procedure

   Definition of a new transfer encoding starts with the publication of
   the specification as an Internet Draft.  The draft MUST define the
   transfer encoding precisely and completely, and it MUST also provide
   substantial justification for defining and standardizing a new
   transfer encoding.  This specification MUST then be presented to the
   IESG for consideration.  The IESG can:

   o  reject the specification outright as being inappropriate for
      standardization,

   o  assign the specification to an existing IETF working group for
      further work,

   o  approve the formation of an IETF working group to work on the
      specification in accordance with IETF procedures, or

   o  accept the specification as-is for processing as an individual
      standards-track submission.

   Transfer encoding specifications on the standards track follow normal
   IETF rules for standards-track documents.  A transfer encoding is

   considered to be defined and available for use once it is on the
   standards track.

3.3.  IANA Procedures for Transfer Encoding Registration

   There is no need for a special procedure for registering Transfer
   Encodings with the IANA.  All legitimate transfer encoding
   registrations MUST appear as a standards-track RFC, so it is the
   IESG's responsibility to notify the IANA when a new transfer encoding
   has been approved.

3.4.  Location of Registered Transfer Encodings List

   The list of transfer encoding registrations can be found at:

     http://www.iana.org/assignments/transfer-encodings

4.  Security Considerations

   Security requirements for access types are discussed in Section
   2.1.4.  Security requirements for transfer encodings are discussed in
   Section 3.1.7.

5.  IANA Considerations

   The sole purpose of this document is to define IANA registries for
   access types and transfer encodings.  The IANA procedures for these
   registries are specified in Section 2.4 and Section 3.3 respectively.

6.  Acknowledgements

   The current authors would like to acknowledge their debt to the late
   Dr. Jon Postel, whose general model of IANA registration procedures
   and specific contributions shaped the predecessors of this document
   [RFC2048].  We hope that the current version is one with which he
   would have agreed but, as it is impossible to verify that agreement,
   we have regretfully removed his name as a co-author.

7.  References

7.1.  Normative References

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              November 1996.

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

   [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
              Registration Procedures", BCP 13, RFC 4288, December 2005.

7.2.  Informative References

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [RFC2048]  Freed, N., Klensin, J., and J. Postel, "Multipurpose
              Internet Mail Extensions (MIME) Part Four: Registration
              Procedures", BCP 13, RFC 2048, November 1996.

   [RFC2278]  Freed, N. and J. Postel, "IANA Charset Registration
              Procedures", BCP 19, RFC 2278, January 1998.

Appendix A.  Changes Since RFC 2048

   o  Media type registration procedures are now described in a separate
      document [RFC4288].

   o  The various URLs and addresses in this document have been changed
      so they all refer to iana.org rather than isi.edu.  Additionally,
      many of the URLs have been changed to use HTTP; formerly they used
      FTP.

   o  Much of the document has been clarified in the light of
      operational experience with these procedures.

   o  Several of the references in this document have been updated to
      refer to current versions of the relevant specifications.

   o  The option of assigning the task of working on a new transfer
      encoding to an existing working group has been added to the list
      of possible actions the IESG can take.

   o  Security considerations and IANA considerations sections have been
      added.

   o  Registration of charsets for use in MIME is specified in [RFC2278]
      and is no longer addressed by this document.

Authors' Addresses

   Ned Freed
   Sun Microsystems
   3401 Centrelake Drive, Suite 410
   Ontario, CA  92761-1205
   USA

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