media type
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Historical Note: The registration process for media types was
initially defined in the context of the asynchronous ...
... 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 ...
... interoperability when the capabilities of the remote mail system are
not known. As media types are used in new environments, where the
proliferation of media types is not a hindrance to interoperability ...
... not known. As media types are used in new environments, where the
proliferation of media types is not a hindrance to interoperability,
the original procedure was excessively restrictive and had to be
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... Media Type Registration ...
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Registration of a new media type or types starts with the
construction of a registration proposal ...
... 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
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... tree.subtree...type"). 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 ...
... tree requires approval
by the IESG and publication of the media type registration as some
form of RFC.
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The vendor tree is used for media types associated with commercially
available products. "Vendor" or "producer ...
... facet "vnd.". That may be followed, at the discretion of the
registration, by either a media type name from a well-known producer
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... IANA-approved designation of the
producer's name which is then followed by a media type or product
designation (e.g., vnd.bigcompany.funnypictures).
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While public exposure and review of media types to be registered in
the vendor tree is not required, using the ietf-types ...
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Registrations for media types created experimentally or as part of
products that are not distributed commercially may be registered in
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While public exposure and review of media types to be registered in
the personal tree is not required, using the ietf-types ...
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For convenience and symmetry with this registration scheme, media
type names with "x." as the first facet may be used for the same
purposes for which names starting in "x-" are normally used. These
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... management by well-known
permanent bodies, such as scientific societies for media types
specific to the sciences they cover. In general, the quality of
review of specifications for one of these additional registration
trees ...
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Media type registration proposals are all expected to conform to
various requirements laid out in the following sections. Note that
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All registered media types must be assigned MIME type and subtype
names. The combination of these names then serves to uniquely
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... MIME type and subtype
names. The combination of these names then serves to uniquely
identify the media type and the format of the subtype name identifies
the registration tree ...
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The choice of top-level type name must take the nature of media type
involved into account. For example, media normally used for
representing still images ...
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In some cases a new media type may not "fit" under any currently
defined top-level content type ...
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Media types may elect to use one or more MIME content type
parameters, or some parameters may be automatically made available to
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... MIME content 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
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... 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 IETF tree,
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... IETF tree,
and should be specified as completely as possible when media types
are registered in the vendor or personal trees ...
... external specification such as JPEG. Similar behavior is encouraged
for media types registered in the vendor or personal trees but is not
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All registered media types must employ a single, canonical data
format, regardless of registration tree.
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A precise and openly available specification of the format of each
media type is required for all types registered in the IETF tree and
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... tree and
must at a minimum be referenced by, if it isn't actually included in,
the media type registration proposal itself.
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The specifications of format and processing particulars may or may
not be publically available for media types registered in the vendor
tree, and such registration proposals are explicitly permitted to
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... include only a specification of which software and version produce or
process such media types. References to or inclusion of format
specifications in registration proposals is encouraged but not
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... 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 RFC
1602(-> 2026) ...
... 1602(-> 2026) on the use of patented technology in standards-track protocols
must be respected when the specification of a media type is part of a
standards-track protocol.
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Media types should, whenever possible, interoperate across as many
systems and applications as possible. However, some media types will
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... Media types should, whenever possible, 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 ...
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Universal interoperability of media types is not required, but known
interoperability issues should be identified whenever possible.
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... interoperability issues should be identified whenever possible.
Publication of a media type does not require an exhaustive review of
interoperability, and the interoperability ...
... requirements for all IETF protocols.) A similar analysis for media
types registered in the vendor or personal trees is encouraged but
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There is absolutely no requirement that media types registered in any
tree be secure or completely free from risks. Nevertheless, all
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... security risks must be identified in the registration of a
media type, again regardless of registration tree.
...
... subject
to continuing evaluation and modification, and in particular may be
extended by use of the "comments on media types" mechanism described
in subsequent sections.
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... Some of the issues that should be looked at in a security analysis of
a media type are:
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... Complex media types may include provisions for
directives that institute actions on a recipient's
files or other resources. In many cases provision is
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... registration of the
application/postscript media type in RFC 2046draft for
an example of such directives and how to handle them.
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... Complex media types may include provisions for
directives that institute actions which, while not
directly harmful to the recipient, may result in
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... registration of the
application/postscript media type illustrates how such
directives can be handled.
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... A media type might be targeted for applications that
require some sort of security assurance but not provide
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... the necessary security mechanisms themselves. For
example, a media type could be defined for storage of
confidential medical information which in turn requires
an external confidentiality service ...
... sender, maximum interoperability is attained by restricting the
number of 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 ...
... 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 resulted in a
registration process with a significant hurdle and delay for those
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... registration process with a significant hurdle and delay for those
registering media types.
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However, the need for "common" media types does not require limiting
the registration of new media types ...
... 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
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... 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 ...
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As such, universal support and implementation of a media type is NOT
a requirement for registration ...
... a requirement for registration. If, however, a media type is
explicitly intended for limited use, this should be noted in its
registration ...
... tree must be
published as RFCs. RFC publication of vendor and personal media type
proposals is encouraged but not required. In all cases IANA will
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... proposals is encouraged but not required. In all cases IANA will
retain copies of all media type proposals and "publish" them as part
of the media types registration tree ...
... retain copies of all media type proposals and "publish" them as part
of the media types registration tree itself.
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... IETF standards process. This is too difficult and too
lengthy a process for the convenient registration of media types.
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... The IETF tree exists for media types that do require require a
substantive review and approval process with the vendor and personal
trees ...
... personal
trees exist for those that do not. It is expected that applicability
statements for particular applications will be published from time to
time that recommend implementation of, and support for, media types
that have proven particularly useful in those contexts.
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Various sorts of optional information may be included in the
specification of a media type if it is available:
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... Magic numbers
are byte sequences that are always present and thus can
be used to identify entities as being of a given media
type.
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... The following procedure has been implemented by the IANA for review
and approval of new media types. This is not a formal standards
process, but rather an administrative procedure intended to allow
community comment and sanity checking without excessive time delay.
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... IANA (at iana@iana.org). However, authors of vendor or
personal media type specifications are encouraged to seek community
review and comment whenever that is feasible.
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... Present the Media Type to the Community for Review ...
... been established for the purpose of reviewing proposed media and
access types. Proposed media types are not formally registered and
must not be used; the "x-" prefix specified in RFC 2045draft ...
... Provided that the media type meets the requirements for media types
and has obtained approval that is necessary, the author may submit
the registration request ...
... registration request to the IANA, which will register the media
type and make the media type registration available to the community.
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... IANA, which will register the media
type and make the media type registration available to the community.
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... Comments on Media Type Registrations ...
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Comments on registered media types may be submitted by members of the
community to IANA. These comments will be passed on to the "owner"
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... community to IANA. These comments will be 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,
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... of the media type if possible. Submitters of comments may request
that their comment be attached to the media type registration itself,
and if IANA approves of this the comment will be made accessible in
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Media type registrations will be posted in the anonymous FTP
directory "ftp://ftp.isi.edu/in-notes/iana/assignments/media-types ...
... directory "ftp://ftp.isi.edu/in-notes/iana/assignments/media-types/"
and all registered media types will be listed in the periodically
issued "Assigned Numbers" RFC [currently STD 2, RFC 1700hist(-> 3232) ...
... issued "Assigned Numbers" RFC [currently STD 2, RFC 1700hist(-> 3232)]. The media
type description and other supporting material may also be published
as an Informational RFC by sending it to "rfc-editor@isi.edu" (please
follow the instructions to RFC authors [RFC-1543(-> 2223) ...
... IANA Procedures for Registering Media Types ...
... All media types must have properly formed type and
subtype names. All type names must be defined by a
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... IANA to conduct a comprehensive security review of
media type registrations. Nevertheless, IANA has the
authority ...
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Once a media type has been published by IANA, the author may request
a change to its definition. The descriptions of the different
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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 ...
... Media type registrations may not be deleted; media types which are no
longer believed appropriate for use can be declared OBSOLETE by a
change to their "intended use" field; such media types ...
... media types which 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 IANA.
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... Published specification:
Applications which use this media type:
Additional information:
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... 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.
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Transfer encodings are tranformations applied to MIME media types
after conversion to the media type's canonical form ...
... Transfer encodings are tranformations applied to MIME media types
after conversion to the media type's canonical form. Transfer
encodings are used for several purposes:
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... Appendix A -- Grandfathered Media Types ...
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A number of media types, registered prior to 1996, would, if
registered under the guidelines in this document, be placed into
either the vendor ...