[Note that this file is a concatenation of more than one RFC.]
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
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
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
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
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
|
