<pre>Network Working Group                                           N. Freed
Request for Comments: 4288                              Sun Microsystems
BCP: 13                                                       J. Klensin
Obsoletes: <a href="./rfc2048">2048</a>                                            December 2005
Category: Best Current Practice


         <span class="h1">Media Type Specifications and Registration Procedures</span>

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.



























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Table of Contents

   <a href="#section-1">1</a>. Introduction ....................................................<a href="#page-3">3</a>
   <a href="#section-2">2</a>. Media Type Registration Preliminaries ...........................<a href="#page-4">4</a>
   <a href="#section-3">3</a>. Registration Trees and Subtype Names ............................<a href="#page-4">4</a>
      <a href="#section-3.1">3.1</a>. Standards Tree .............................................<a href="#page-4">4</a>
      <a href="#section-3.2">3.2</a>. Vendor Tree ................................................<a href="#page-5">5</a>
      <a href="#section-3.3">3.3</a>. Personal or Vanity Tree ....................................<a href="#page-5">5</a>
      <a href="#section-3.4">3.4</a>. Special x. Tree ............................................<a href="#page-5">5</a>
      <a href="#section-3.5">3.5</a>. Additional Registration Trees ..............................<a href="#page-6">6</a>
   <a href="#section-4">4</a>. Registration Requirements .......................................<a href="#page-6">6</a>
      <a href="#section-4.1">4.1</a>. Functionality Requirement ..................................<a href="#page-6">6</a>
      <a href="#section-4.2">4.2</a>. Naming Requirements ........................................<a href="#page-6">6</a>
         <a href="#section-4.2.1">4.2.1</a>. Text Media Types ......................................<a href="#page-7">7</a>
         <a href="#section-4.2.2">4.2.2</a>. Image Media Types .....................................<a href="#page-8">8</a>
         <a href="#section-4.2.3">4.2.3</a>. Audio Media Types .....................................<a href="#page-8">8</a>
         <a href="#section-4.2.4">4.2.4</a>. Video Media Types .....................................<a href="#page-8">8</a>
         <a href="#section-4.2.5">4.2.5</a>. Application Media Types ...............................<a href="#page-9">9</a>
         <a href="#section-4.2.6">4.2.6</a>. Multipart and Message Media Types .....................<a href="#page-9">9</a>
         <a href="#section-4.2.7">4.2.7</a>. Additional Top-level Types ............................<a href="#page-9">9</a>
      <a href="#section-4.3">4.3</a>. Parameter Requirements ....................................<a href="#page-10">10</a>
      <a href="#section-4.4">4.4</a>. Canonicalization and Format Requirements ..................<a href="#page-10">10</a>
      <a href="#section-4.5">4.5</a>. Interchange Recommendations ...............................<a href="#page-11">11</a>
      <a href="#section-4.6">4.6</a>. Security Requirements .....................................<a href="#page-11">11</a>
      <a href="#section-4.7">4.7</a>. Requirements specific to XML media types ..................<a href="#page-13">13</a>
      <a href="#section-4.8">4.8</a>. Encoding Requirements .....................................<a href="#page-13">13</a>
      <a href="#section-4.9">4.9</a>. Usage and Implementation Non-requirements .................<a href="#page-13">13</a>
      <a href="#section-4.10">4.10</a>. Publication Requirements .................................<a href="#page-14">14</a>
      <a href="#section-4.11">4.11</a>. Additional Information ...................................<a href="#page-15">15</a>
   <a href="#section-5">5</a>. Registration Procedure .........................................<a href="#page-15">15</a>
      <a href="#section-5.1">5.1</a>. Preliminary Community Review ..............................<a href="#page-16">16</a>
      <a href="#section-5.2">5.2</a>. IESG Approval .............................................<a href="#page-16">16</a>
      <a href="#section-5.3">5.3</a>. IANA Registration .........................................<a href="#page-16">16</a>
      <a href="#section-5.4">5.4</a>. Media Types Reviewer ......................................<a href="#page-16">16</a>
   <a href="#section-6">6</a>. Comments on Media Type Registrations ...........................<a href="#page-17">17</a>
   <a href="#section-7">7</a>. Location of Registered Media Type List .........................<a href="#page-17">17</a>
   <a href="#section-8">8</a>. IANA Procedures for Registering Media Types ....................<a href="#page-17">17</a>
   <a href="#section-9">9</a>. Change Procedures ..............................................<a href="#page-18">18</a>
   <a href="#section-10">10</a>. Registration Template .........................................<a href="#page-19">19</a>
   <a href="#section-11">11</a>. Security Considerations .......................................<a href="#page-20">20</a>
   <a href="#section-12">12</a>. IANA Considerations ...........................................<a href="#page-20">20</a>
   <a href="#section-13">13</a>. Acknowledgements ..............................................<a href="#page-20">20</a>
   <a href="#section-14">14</a>. References ....................................................<a href="#page-20">20</a>
   <a href="#appendix-A">Appendix A</a>.  Grandfathered Media Types ............................<a href="#page-22">22</a>
   <a href="#appendix-B">Appendix B</a>.  Changes Since <a href="./rfc2048">RFC 2048</a> ...............................<a href="#page-22">22</a>






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<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>.  Introduction</span>

   Recent Internet protocols have been carefully designed to be easily
   extensible in certain areas.  In particular, many protocols,
   including but not limited to MIME [<a href="./rfc2045" title="&quot;Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies&quot;">RFC2045</a>], 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 [<a href="./rfc2048" title="&quot;Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures&quot;">RFC2048</a>], 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 <a href="#section-4.9">Section 4.9</a> for additional discussion.

<span class="h3"><a class="selflink" id="section-1.1" href="#section-1.1">1.1</a>.  Conventions Used in This Document</span>

   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 [<a href="./rfc2119" title="&quot;Key words for use in RFCs to Indicate Requirement Levels&quot;">RFC2119</a>].

   This specification makes use of the Augmented Backus-Naur Form (ABNF)
   [<a href="./rfc4234" title="&quot;Augmented BNF for Syntax Specifications: ABNF&quot;">RFC4234</a>] notation, including the core rules defined in <a href="#appendix-A">Appendix A</a> of
   that document.






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<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>.  Media Type Registration Preliminaries</span>

   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.

<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>.  Registration Trees and Subtype Names</span>

   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 <a href="#appendix-A">Appendix A</a> for a discussion of them.

<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a>.  Standards Tree</span>

   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.







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<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>.  Vendor Tree</span>

   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.

<span class="h3"><a class="selflink" id="section-3.3" href="#section-3.3">3.3</a>.  Personal or Vanity Tree</span>

   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.

<span class="h3"><a class="selflink" id="section-3.4" href="#section-3.4">3.4</a>.  Special x. Tree</span>

   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



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   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.

<span class="h3"><a class="selflink" id="section-3.5" href="#section-3.5">3.5</a>.  Additional Registration Trees</span>

   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.

<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>.  Registration Requirements</span>

   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.

<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a>.  Functionality Requirement</span>

   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 [<a href="./rfc2045" title="&quot;Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies&quot;">RFC2045</a>], base64 cannot be registered as a
   media type.

   This requirement applies regardless of the registration tree
   involved.

<span class="h3"><a class="selflink" id="section-4.2" href="#section-4.2">4.2</a>.  Naming Requirements</span>

   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.



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   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 <a href="#section-3.4">Section 3.4</a>.


   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 / "!" /
                       "#" / "$" / "&amp;" / "." /
                       "+" / "-" / "^" / "_"

   Note that this syntax is somewhat more restrictive than what is
   allowed by the ABNF in [<a href="./rfc2045" title="&quot;Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies&quot;">RFC2045</a>].

   In accordance with the rules specified in [<a href="./rfc3023" title="&quot;XML Media Types&quot;">RFC3023</a>], 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 [<a href="./rfc2046" title="&quot;Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types&quot;">RFC2046</a>] for additional
   information on the restrictions MIME imposes.)

<span class="h4"><a class="selflink" id="section-4.2.1" href="#section-4.2.1">4.2.1</a>.  Text Media Types</span>

   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 [<a href="./rfc2046" title="&quot;Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types&quot;">RFC2046</a>].  If defined, a text "charset"




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   parameter MUST be used to specify a charset name defined in
   accordance to the procedures laid out in [<a href="./rfc2978" title="&quot;IANA Charset Registration Procedures&quot;">RFC2978</a>].

   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".

<span class="h4"><a class="selflink" id="section-4.2.2" href="#section-4.2.2">4.2.2</a>.  Image Media Types</span>

   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.

<span class="h4"><a class="selflink" id="section-4.2.3" href="#section-4.2.3">4.2.3</a>.  Audio Media Types</span>

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

<span class="h4"><a class="selflink" id="section-4.2.4" href="#section-4.2.4">4.2.4</a>.  Video Media Types</span>

   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".



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<span class="h4"><a class="selflink" id="section-4.2.5" href="#section-4.2.5">4.2.5</a>.  Application Media Types</span>

   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 [<a href="./rfc2046" title="&quot;Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types&quot;">RFC2046</a>].)

   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".

<span class="h4"><a class="selflink" id="section-4.2.6" href="#section-4.2.6">4.2.6</a>.  Multipart and Message Media Types</span>

   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 [<a href="./rfc2046" title="&quot;Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types&quot;">RFC2046</a>].

<span class="h4"><a class="selflink" id="section-4.2.7" href="#section-4.2.7">4.2.7</a>.  Additional Top-level Types</span>

   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.





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<span class="h3"><a class="selflink" id="section-4.3" href="#section-4.3">4.3</a>.  Parameter Requirements</span>

   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 [<a href="./rfc2045" title="&quot;Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies&quot;">RFC2045</a>] and amended by [<a href="./rfc2231" title="&quot;MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations&quot;">RFC2231</a>].

   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.

<span class="h3"><a class="selflink" id="section-4.4" href="#section-4.4">4.4</a>.  Canonicalization and Format Requirements</span>

   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



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   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
   [<a href="./rfc2026" title="&quot;The Internet Standards Process -- Revision 3&quot;">RFC2026</a>] 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.

<span class="h3"><a class="selflink" id="section-4.5" href="#section-4.5">4.5</a>.  Interchange Recommendations</span>

   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.

<span class="h3"><a class="selflink" id="section-4.6" href="#section-4.6">4.6</a>.  Security Requirements</span>

   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




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   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 <a href="#section-6">Section 6</a> 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 [<a href="./rfc2046" title="&quot;Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types&quot;">RFC2046</a>] 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




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

<span class="h3"><a class="selflink" id="section-4.7" href="#section-4.7">4.7</a>.  Requirements specific to XML media types</span>

   There are a number of additional requirements specific to the
   registration of XML media types.  These requirements are specified in
   [<a href="./rfc3023" title="&quot;XML Media Types&quot;">RFC3023</a>].

<span class="h3"><a class="selflink" id="section-4.8" href="#section-4.8">4.8</a>.  Encoding Requirements</span>

   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 [<a href="./rfc3555" title="&quot;MIME Type Registration of RTP Payload Formats&quot;">RFC3555</a>].

   Additional restrictions on 7bit and 8bit text are given in [<a href="./rfc2046" title="&quot;Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types&quot;">RFC2046</a>].

<span class="h3"><a class="selflink" id="section-4.9" href="#section-4.9">4.9</a>.  Usage and Implementation Non-requirements</span>

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



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   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.

<span class="h3"><a class="selflink" id="section-4.10" href="#section-4.10">4.10</a>.  Publication Requirements</span>

   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 <a href="#section-10">Section 10</a>.  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



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   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.

<span class="h3"><a class="selflink" id="section-4.11" href="#section-4.11">4.11</a>.  Additional Information</span>

   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 [<a href="./rfc3986" title="&quot;Uniform Resource Identifier (URI): Generic Syntax&quot;">RFC3986</a>] 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.

<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>.  Registration Procedure</span>

   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



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

<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>.  Preliminary Community Review</span>

   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.

<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>.  IESG Approval</span>

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

<span class="h3"><a class="selflink" id="section-5.3" href="#section-5.3">5.3</a>.  IANA Registration</span>

   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:

     <a href="http://www.iana.org/cgi-bin/mediatypes.pl">http://www.iana.org/cgi-bin/mediatypes.pl</a>

   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.

<span class="h3"><a class="selflink" id="section-5.4" href="#section-5.4">5.4</a>.  Media Types Reviewer</span>

   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.



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   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 <a href="./rfc2026#section-6.5.4">[RFC2026] section&nbsp;6.5.4</a>.

   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.

<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>.  Comments on Media Type Registrations</span>

   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.

<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>.  Location of Registered Media Type List</span>

   Media type registrations are listed by the IANA at:

      <a href="http://www.iana.org/assignments/media-types/">http://www.iana.org/assignments/media-types/</a>

<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>.  IANA Procedures for Registering Media Types</span>

   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.






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   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.

<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>.  Change Procedures</span>

   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.












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<span class="h2"><a class="selflink" id="section-10" href="#section-10">10</a>.  Registration Template</span>

   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 &amp; 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 [<a href="#ref-MacOSFileTypes" title="&quot;Mac OS: File Type and Creator Codes, and File Formats&quot;">MacOSFileTypes</a>].  Additionally, please refrain from writing



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

<span class="h2"><a class="selflink" id="section-11" href="#section-11">11</a>.  Security Considerations</span>

   Security requirements for media type registrations are discussed in
   <a href="#section-4.6">Section 4.6</a>.

<span class="h2"><a class="selflink" id="section-12" href="#section-12">12</a>.  IANA Considerations</span>

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

<span class="h2"><a class="selflink" id="section-13" href="#section-13">13</a>.  Acknowledgements</span>

   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
   [<a href="./rfc2048" title="&quot;Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures&quot;">RFC2048</a>].  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.

<span class="h2"><a class="selflink" id="section-14" href="#section-14">14</a>.  References</span>

<span class="h3"><a class="selflink" id="section-14.1" href="#section-14.1">14.1</a>.  Normative References</span>

   [<a id="ref-RFC2045">RFC2045</a>]        Freed, N. and N. Borenstein, "Multipurpose Internet
                    Mail Extensions (MIME) Part One: Format of Internet
                    Message Bodies", <a href="./rfc2045">RFC 2045</a>, November 1996.

   [<a id="ref-RFC2046">RFC2046</a>]        Freed, N. and N. Borenstein, "Multipurpose Internet
                    Mail Extensions (MIME) Part Two: Media Types", <a href="./rfc2046">RFC</a>
                    <a href="./rfc2046">2046</a>, November 1996.

   [<a id="ref-RFC2119">RFC2119</a>]        Bradner, S., "Key words for use in RFCs to Indicate
                    Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.

   [<a id="ref-RFC2978">RFC2978</a>]        Freed, N. and J. Postel, "IANA Charset Registration
                    Procedures", <a href="https://www.rfc-editor.org/bcp/bcp19">BCP 19</a>, <a href="./rfc2978">RFC 2978</a>, October 2000.

   [<a id="ref-RFC3023">RFC3023</a>]        Murata, M., St. Laurent, S., and D. Kohn, "XML Media
                    Types", <a href="./rfc3023">RFC 3023</a>, January 2001.

   [<a id="ref-RFC3555">RFC3555</a>]        Casner, S. and P. Hoschka, "MIME Type Registration
                    of RTP Payload Formats", <a href="./rfc3555">RFC 3555</a>, July 2003.






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   [<a id="ref-RFC3986">RFC3986</a>]        Berners-Lee, T., Fielding, R., and L. Masinter,
                    "Uniform Resource Identifier (URI): Generic Syntax",
                    STD 66, <a href="./rfc3986">RFC 3986</a>, January 2005.

   [<a id="ref-RFC4234">RFC4234</a>]        Crocker, D. Ed., and P. Overell, "Augmented BNF for
                    Syntax Specifications: ABNF", <a href="./rfc4234">RFC 4234</a>, October
                    2005.

<span class="h3"><a class="selflink" id="section-14.2" href="#section-14.2">14.2</a>.  Informative References</span>

   [<a id="ref-MacOSFileTypes">MacOSFileTypes</a>] Apple Computer, Inc., "Mac OS: File Type and Creator
                    Codes, and File Formats", Apple Knowledge Base
                    Article 55381, June 1993,
                    &lt;<a href="http://www.info.apple.com/kbnum/n55381">http://www.info.apple.com/kbnum/n55381</a>&gt;.

   [<a id="ref-RFC2026">RFC2026</a>]        Bradner, S., "The Internet Standards Process --
                    Revision 3", <a href="https://www.rfc-editor.org/bcp/bcp9">BCP 9</a>, <a href="./rfc2026">RFC 2026</a>, October 1996.

   [<a id="ref-RFC2048">RFC2048</a>]        Freed, N., Klensin, J., and J. Postel, "Multipurpose
                    Internet Mail Extensions (MIME) Part Four:
                    Registration Procedures", <a href="https://www.rfc-editor.org/bcp/bcp13">BCP 13</a>, <a href="./rfc2048">RFC 2048</a>, November
                    1996.

   [<a id="ref-RFC2231">RFC2231</a>]        Freed, N. and K. Moore, "MIME Parameter Value and
                    Encoded Word Extensions: Character Sets, Languages,
                    and Continuations", <a href="./rfc2231">RFC 2231</a>, November 1997.

























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<span class="grey"><a href="./rfc4288">RFC 4288</a>                Media Type Registration            December 2005</span>


<span class="h2"><a class="selflink" id="appendix-A" href="#appendix-A">Appendix A</a>.  Grandfathered Media Types</span>

   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.

<span class="h2"><a class="selflink" id="appendix-B" href="#appendix-B">Appendix B</a>.  Changes Since <a href="./rfc2048">RFC 2048</a></span>

   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  <a href="./rfc3023">RFC 3023</a> 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.







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<span class="grey"><a href="./rfc4288">RFC 4288</a>                Media Type Registration            December 2005</span>


   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 <a href="./rfc2046">RFC 2046</a> 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








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<span class="grey"><a href="./rfc4288">RFC 4288</a>                Media Type Registration            December 2005</span>


Full Copyright Statement

   Copyright (C) The Internet Society (2005).

   This document is subject to the rights, licenses and restrictions
   contained in <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a>, and except as set forth therein, the authors
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   such proprietary rights by implementers or users of this
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   The IETF invites any interested party to bring to its attention any
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Acknowledgement

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







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