Network Working Group M. Nottingham
Internet-Draft Cloudflare
Obsoletes: 6838 (if approved) P. Resnick
Intended status: Best Current Practice 23 May 2025
Expires: 24 November 2025
Media Type Specifications and Registration Procedures
draft-ietf-mediaman-6838bis-04
Abstract
This document defines procedures for the specification and
registration of media types for use in HTTP, MIME, and other Internet
protocols.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-mediaman-6838bis/.
information can be found at https://datatracker.ietf.org/wg/mediaman/
about/.
Source for this draft and an issue tracker can be found at
https://github.com/ietf-wg-mediaman/6838bis/.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 24 November 2025.
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Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions Used in This Document . . . . . . . . . . . . 4
2. Media Type Registration Requirements . . . . . . . . . . . . 4
2.1. Functionality . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Publication . . . . . . . . . . . . . . . . . . . . . . . 4
2.2.1. Specification Availability . . . . . . . . . . . . . 5
2.2.2. Intellectual Property . . . . . . . . . . . . . . . . 5
2.3. Canonicalization and Interoperability . . . . . . . . . . 5
2.4. Naming . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4.1. Aliases . . . . . . . . . . . . . . . . . . . . . . . 7
2.5. Parameters . . . . . . . . . . . . . . . . . . . . . . . 7
2.6. Encoding . . . . . . . . . . . . . . . . . . . . . . . . 8
2.7. Fragment Identifiers . . . . . . . . . . . . . . . . . . 9
2.8. Security . . . . . . . . . . . . . . . . . . . . . . . . 9
2.8.1. Structured Suffixes . . . . . . . . . . . . . . . . . 10
2.9. Additional Information . . . . . . . . . . . . . . . . . 12
2.10. Non-Requirements . . . . . . . . . . . . . . . . . . . . 12
3. Top-Level Media Types . . . . . . . . . . . . . . . . . . . . 13
3.1. Text Media Types . . . . . . . . . . . . . . . . . . . . 13
3.1.1. The Charset Parameter . . . . . . . . . . . . . . . . 14
3.2. Image Media Types . . . . . . . . . . . . . . . . . . . . 14
3.3. Audio Media Types . . . . . . . . . . . . . . . . . . . . 14
3.4. Video Media Types . . . . . . . . . . . . . . . . . . . . 14
3.5. Application Media Types . . . . . . . . . . . . . . . . . 15
3.6. Multipart and Message Media Types . . . . . . . . . . . . 15
3.7. Additional Top-Level Types . . . . . . . . . . . . . . . 16
3.7.1. Required Criteria . . . . . . . . . . . . . . . . . . 16
3.7.2. Additional Considerations . . . . . . . . . . . . . . 16
3.7.3. Negative Criteria . . . . . . . . . . . . . . . . . . 18
4. Media Subtypes . . . . . . . . . . . . . . . . . . . . . . . 18
4.1. Registration Trees . . . . . . . . . . . . . . . . . . . 18
4.1.1. Standards Tree . . . . . . . . . . . . . . . . . . . 19
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4.1.2. Vendor Tree . . . . . . . . . . . . . . . . . . . . . 20
4.1.3. Personal Tree . . . . . . . . . . . . . . . . . . . . 21
4.1.4. Unregistered x. Tree . . . . . . . . . . . . . . . . 22
4.1.5. Additional Registration Trees . . . . . . . . . . . . 22
4.2. Subtype Suffixes . . . . . . . . . . . . . . . . . . . . 22
4.2.1. Common Suffix Patterns . . . . . . . . . . . . . . . 23
4.2.2. Fragment Identifiers and Suffixes . . . . . . . . . . 24
5. Media Type Registration Procedures . . . . . . . . . . . . . 24
5.1. Preliminary Community Review . . . . . . . . . . . . . . 24
5.2. Submit Request to IANA . . . . . . . . . . . . . . . . . 25
5.2.1. Provisional Registrations . . . . . . . . . . . . . . 25
5.3. Review and Approval . . . . . . . . . . . . . . . . . . . 26
5.4. Comments on Media Type Registrations . . . . . . . . . . 26
5.5. Change Procedures . . . . . . . . . . . . . . . . . . . . 26
5.6. Registration Template . . . . . . . . . . . . . . . . . . 27
6. Structured Syntax Suffix Registration Procedures . . . . . . 28
6.1. Change Procedures . . . . . . . . . . . . . . . . . . . . 29
6.2. Structured Syntax Suffix Registration Template . . . . . 29
7. Security Considerations . . . . . . . . . . . . . . . . . . . 30
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 31
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
10.1. Normative References . . . . . . . . . . . . . . . . . . 31
10.2. Informative References . . . . . . . . . . . . . . . . . 33
Appendix A. Historical Note . . . . . . . . . . . . . . . . . . 34
Appendix B. Grandfathered Media Types . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction
Internet application protocols are capable of carrying arbitrary
labeled content, including but not limited to HTTP [RFC9110] and MIME
[RFC2045].
Such labels are known as media types. A media type consists of a
top-level type and a subtype, which is further structured into trees.
Optionally, a media type can be defined to allow companion data,
known as parameters.
This document defines the criteria and procedures to be used to
register media types (Section 5) as well as media type structured
suffixes (Section 6) in the Internet Assigned Numbers Authority
(IANA) registry.
The location of the media type registry managed by these procedures
is:
http://www.iana.org/assignments/media-types/
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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] when they
appear in ALL CAPS. They may also appear in lower or mixed case as
plain English words, without any normative meaning.
This specification makes use of the Augmented Backus-Naur Form (ABNF)
[RFC5234] notation, including the core rules defined in Appendix B of
that document.
2. Media Type Registration Requirements
Media type registrations are expected to conform to various
requirements laid out in the following sections. Note that specific
requirements can vary depending on the registration tree
(Section 4.1).
Additional requirements specific to the registration of XML media
types are specified in [RFC7303].
2.1. Functionality
Media types MUST function as actual media formats. 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.
2.2. Publication
Media types registered in the standards tree by the IETF MUST be
published as RFCs. Media types registered in the vendor and personal
trees can be published as RFCs, but this is not required.
Standards-tree registrations for media types defined by other
standards-related organizations MUST be described by a formal
specification produced by that organization.
Other than IETF registrations in the standards tree, the registration
of a media type does not imply endorsement, approval, or
recommendation by the IANA or the IETF or even certification that the
specification is adequate.
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Registration of a new top-level type requires Standards Action in the
IETF and, hence, the publication of a RFC on the Standards Track.
2.2.1. Specification Availability
A permanent and readily available public specification of the format
for the media type MUST exist for all types registered in the
standards tree. This specification MUST provide sufficient detail so
that interoperability between independent implementations using the
media type is possible. If not part of the media type registration
proposal, this specification MUST be referenced by it.
A specification need not be publicly available for media types
registered in the vendor and personal trees. Note, however, that the
public availability of a specification will often make the difference
between having a name reserved and having the potential for useful
interoperation.
2.2.2. Intellectual Property
The registration of media types involving patented technology is
permitted. However, the restrictions set forth in BCP 79 [RFC8179]
and BCP 78 [RFC5378] 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-related organizations making use of the standards
tree may have their own rules regarding intellectual property that
must be observed in their registrations.
Intellectual Property Rights (IPR) disclosures for registrations in
the vendor and personal trees are encouraged but not required.
Copyright on the registration template MUST allow the IANA to copy it
into the IANA registry.
2.3. Canonicalization and Interoperability
All registered media types MUST employ a single, canonical data
format, regardless of registration tree.
Ideally, media types will be defined so they interoperate across as
many systems and applications as possible. However, some media types
will inevitably have problems interoperating across different
platforms. For example, problems with different versions, byte
ordering, and specifics of gateway handling can arise.
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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.
The recommendations in this subsection apply regardless of the
registration tree involved.
2.4. Naming
All registered media types MUST be assigned top-level type and
subtype names. The combination of these names serves to uniquely
identify the media type, and the subtype name facet (or the absence
of one) identifies the registration tree. Both top-level type and
subtype names are case-insensitive.
Type and subtype names MUST conform to the following ABNF:
type-name = restricted-name
subtype-name = restricted-name
restricted-name = restricted-name-first *126restricted-name-chars
restricted-name-first = ALPHA / DIGIT
restricted-name-chars = ALPHA / DIGIT / "!" / "#" /
"$" / "&" / "-" / "^" / "_"
restricted-name-chars =/ "." ; Characters before first dot always
; specify a facet name
restricted-name-chars =/ "+" ; Characters after last plus always
; specify a structured syntax suffix
Note that this syntax is somewhat more restrictive than what is
allowed by Section 5.1 of [RFC2045] or Section 4.2 of [RFC4288].
Also note that while this syntax allows names of up to 127
characters, implementation limits may make such long names
problematic. For this reason, 'type-name' and 'subtype-name' SHOULD
be limited to 64 characters.
Although this syntax treats "." as equivalent to any other character,
characters before any initial "." always specify the registration
facet. Note that this means that facet-less standards tree
registrations cannot use periods in the subtype name.
Similarly, the final "+" in a subtype name introduces a structured
syntax specifier suffix. Structured syntax suffix requirements are
specified in Section 4.2.
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While it is possible for a given media type to be assigned more than
one name, the use of different names to identify the same media type
is discouraged.
These requirements apply regardless of the registration tree
involved.
2.4.1. Aliases
In some cases, a single media type may have been widely deployed
prior to registration under multiple names. In such cases, a
preferred name MUST be chosen for the media type, and applications
MUST use this to be compliant with the type's registration. However,
a list of deprecated aliases by which the type is known MAY be
supplied as additional information in order to assist applications in
processing the media type properly.
2.5. Parameters
Media types MAY be defined to allow or require use of media type
parameters. Additionally, 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 same syntax as media type names and values:
parameter-name = restricted-name
Note that this syntax is somewhat more restrictive than what is
allowed by the ABNF in [RFC2045] and amended by [RFC2231].
Parameter names are case-insensitive and no meaning is attached to
the order in which they appear. It is an error for a specific
parameter to be specified more than once.
There is no defined syntax for parameter values; therefore, it MUST
be specified upon registration. Additionally, some transports impose
restrictions on parameter value syntax, so care needs be taken to
limit the use of potentially problematic syntaxes; for example,
binary valued parameters, while permitted in some protocols, are best
avoided.
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Note that a protocol can impose further restrictions on parameter
value syntax, depending on how it chooses to represent parameters.
Both MIME [RFC2045] [RFC2231] and HTTP [RFC9110] [RFC8187] allow
binary parameters as well as parameter values expressed in a specific
charset, but other protocols may be less flexible.
Types already registered in the standards tree SHOULD NOT have new
functionality added through the definition of new parameters
subsequent to the original registration. New parameters MAY be used
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.
Changes to parameters (including the introduction of new ones) is
managed in the same manner as other changes to the media type; see
Section 5.5.
2.6. Encoding
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.
An "encoding considerations" field is provided to note what sort of
data a media type can consist of as part of its registration.
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 an unrestricted sequence of octets.
framed: The content consists of a series of frames or packets
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without internal framing or alignment indicators. Additional out-
of-band information is needed to interpret the data properly,
including but not limited to knowledge of the boundaries between
successive frames and knowledge of the transport mechanism. Note
that media types of this sort cannot be stored in a file or
transported as a stream of octets without further context;
therefore, such media types are thus 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 [RFC4855].
Additional restrictions on 7bit and 8bit text are given in
Section 4.1.1 of [RFC2046].
2.7. Fragment Identifiers
Media type registrations can specify how applications should
interpret fragment identifiers (specified in Section 3.5 of
[RFC3986]) associated with the media type.
Media types are encouraged to adopt fragment identifier schemes that
are used with semantically similar media types. In particular, media
types that use a named structured syntax with a registered "+suffix"
MUST follow whatever fragment identifier rules are given in the
structured syntax suffix registration.
2.8. Security
All registrations of types in the standards tree MUST include an
analysis of security issues. A similar analysis for media types
registered in the vendor or personal trees is encouraged but not
required.
All descriptions of security issues MUST be as accurate as possible
regardless of registration tree. In particular, the security
considerations MUST NOT state that there are "no security issues
associated with this type". Security considerations for types in the
vendor or personal tree MAY say that "the security issues associated
with this type have not been assessed".
There is 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.
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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 5.4 below.
Issues that need to be described in a security analysis of a media
type include:
* Processing of complex media types might institute actions on a
recipient's files or other resources. If it is possible to
specify arbitrary actions in an unrestricted fashion, it could
have devastating effects. See the registration of the
application/postscript media type in [RFC2046] for an example of
description and handling of these issues.
* Any security analysis MUST state whether or not the format employs
such "active content"; if it does, it MUST state what steps have
been taken (or are required be taken by applications) of the media
type to protect users of the media type.
* Processing of complex media types might 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.
* 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; if they do, they SHOULD discuss what steps
need to be taken to avoid such attacks.
* A media type might be targeted for applications that require some
sort of security assurance but don't provide the necessary
security mechanisms themselves. For example, a media type could
be defined for storage of sensitive medical information that in
turn requires external confidentiality and integrity protection
services, or which is designed for use only within a secure
environment. Types SHOULD always document whether or not they
need such services in their security considerations.
2.8.1. Structured Suffixes
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2.8.1.1. Document Validity
If a toolchain chooses to process a provided media type by using the
selected structured suffix processing rules, it cannot presume that a
document that is valid per the decoding rules associated with the
structured suffix will be valid for a recognized subset of the
structured suffix. For example, presuming a media type of
"application/foo+bar", a toolchain cannot presume that a valid "+bar"
document will also be a valid "application/foo" document. On the
other hand, presuming a media type of "application/foo+bar", a
toolchain can presume that a valid "application/foo+bar" document
will also be a valid "+bar" document.
2.8.1.2. Fragment Semantics
If a toolchain chooses to process a provided media type by using the
selected structured suffix processing rules, it cannot presume that
fragment identifier semantics will be the same across a recognized
subset of the structured suffix. For example, presuming a media type
of "application/foo+bar", a toolchain cannot presume that the
fragment semantics for a "+bar" document will be the same as for an
"application/foo+bar" document.
2.8.1.3. Security Characteristics
Toolchains cannot assume that the security characteristics of
processing based on structured suffixes will be the same for the
entire media type. For example, presuming a media type of
"application/foo+bar", a toolchain cannot presume that the security
characteristics for a "+bar" document will be the same as for a
"application/foo+bar" document.
2.8.1.4. Partial Processing
It is conceivable that an attacker could utilize structured suffixes
in a way that tricks unsuspecting toolchains into skipping important
security checks and allowing viruses to propagate. For example, an
attacker might utilize an "application/vnd.ms-
excel.addin.macroEnabled.12+zip" structured suffix to trigger an
unzip process that might then directly invoke Microsoft Excel,
bypassing anti-virus tooling that would otherwise block a macro-
enabled MS Excel file containing a virus of some kind from being
scanned or opened.
Enterprising attackers might take advantage of toolchains that
partially process media types in this manner. Toolchains that
process media types based purely on a structured suffix need to
ensure that further processing does not blindly trust the decoded
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data, and that proper magic header or file structure checking is
performed, before allowing the decoded data to drive operations that
might negatively impact the application environment or operating
system.
2.9. Additional Information
The following optional information SHOULD be included in the
specification of a media type if it is available:
* 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.
* File name extension(s) commonly used on one or more platforms to
indicate that some file contains a given media type.
* macOS Uniform Type Identifier (a string), if it makes sense to
exchange media of this type through user-triggered exchange
mechanisms such as copy-and-paste or drag-and-drop on macOS and
related platforms (see [MacOSUTIs] for definitions and syntax).
* Windows clipboard name (a string), if it makes sense to exchange
media of this type through user-triggered exchange mechanisms such
as copy-and-paste or drag-and-drop on Microsoft Windows and
related platforms (see [windowsClipboardNames] for definitions and
syntax).
In the case of a registration in the standards tree, this additional
information MAY be provided in the formal specification of the media
type format. It is suggested that this be done by incorporating the
IANA media type registration form into the specification itself.
2.10. Non-Requirements
Universal support and implementation of a media type are NOT a
requirement for registration.
In some environments such as mail, information on the capabilities of
the remote mail agent is frequently not available to the sender.
When this is the case, maximum interoperability might be attained by
restricting the media types used to those "common" formats expected
to be widely implemented.
In the past, this reasoning was used to limit the number of possible
media types, and resulted in a 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. If a limited set of media types
is recommended for a particular application, that should be asserted
by a separate applicability statement specific for that environment.
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.
3. Top-Level Media Types
The choice of top-level type 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 HTTP and MIME, MAY impose
additional restrictions on the media types they can transport. (See
[RFC2046] for additional information on the restrictions MIME
imposes.)
3.1. Text Media Types
A top-level type of "text" indicates that the content is principally
textual in form.
Text that does not provide for or allow formatting commands, font
attribute specifications, processing instructions, interpretation
directives, or content markup is known as "plain text". 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
different 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 can be
represented using subtypes of "text".
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3.1.1. The Charset Parameter
Many subtypes of text, notably including the subtype "text/plain",
which is a generic subtype for plain text defined in [RFC2046],
define a "charset" parameter. If a "charset" parameter is defined
for a particular subtype of text, it MUST be used to specify a
charset name defined in accordance to the procedures laid out in
[RFC2978].
As specified in [RFC6657], a "charset" parameter SHOULD NOT be
specified when charset information is transported inside the payload
(e.g., as in "text/xml").
If a "charset" parameter is specified, it SHOULD be a required
parameter, eliminating the options of specifying a default value. If
there is a strong reason for the parameter to be optional despite
this advice, each subtype MAY specify its own default value, or
alternatively, it MAY specify that there is no default value.
Finally, the "UTF-8" charset [RFC3629] SHOULD be selected as the
default. See [RFC6657] for additional information on the use of
"charset" parameters in conjunction with subtypes of text.
Regardless of what approach is chosen, all new text/* registrations
MUST clearly specify how the charset is determined; relying on the
US-ASCII default defined in Section 4.1.2 of [RFC2046] is no longer
permitted. If explanatory text is needed, this SHOULD be placed in
the additional information section of the registration.
3.2. Image Media Types
A top-level type of "image" indicates that the content is one or more
individual images. The subtype names the specific image format.
3.3. Audio Media Types
A top-level type of "audio" indicates that the content is audio data.
The subtype names the specific audio format.
3.4. Video Media Types
A top-level type of "video" indicates that the content is 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.
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Note that although in general the mixing of multiple kinds of media
in a single body is discouraged [RFC2046], it is recognized that many
video formats include a representation for synchronized audio and/or
text, and this is explicitly permitted for subtypes of "video".
3.5. Application Media Types
A top-level type of "application" indicates that the content is
discrete data that do not fit under any of the other type names, 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" type name include but are not
limited to file transfer, spreadsheets, presentations, scheduling
data, and languages for "active" (computational) material. (The
last, in particular, can pose security problems that must be
understood by implementors. The "application/postscript" media type
registration in [RFC2046] provides a good example of how to handle
these issues.)
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" top-level type.
The subtype of "application" will often either be 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
simply be used freely as a subtype of "application"; the subtype
needs to be registered.
3.6. Multipart and Message Media Types
A top-level type of "multipart" or "message" indicates that the
content is a composite type; that is, they provide a means of
encapsulating zero or more objects, each one a separate media type.
All subtypes of multipart and message MUST conform to the syntax
rules and other requirements specified in [RFC2046] and amended by
Section 3.5 of [RFC6532].
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3.7. Additional Top-Level Types
In some cases, a new media type may not be easily classified under
any currently defined top-level type names. Such cases are expected
to be quite rare. However, if such a case does arise, a new type
name can be defined to accommodate it. Definition of a new top-level
type name MUST be done via a Standards Track RFC, taking into account
the criteria and guidelines given below; no other mechanism can be
used to define additional type names.
3.7.1. Required Criteria
Definitions of new top-level types are required to fulfil the
following criteria:
* Every new top-level type MUST be defined in a Standards Track RFC
(see Section 4.9 of [RFC8126]). This will make sure there is
sufficient community interest, review, and consensus appropriate
for a new top-level type.
* The IANA Considerations section of an RFC defining a new top-level
type MUST request that IANA add this new top-level type to the
registry of top-level types.
* The criteria for what types do and do not fall under the new top-
level type MUST be defined clearly. Clear criteria are expected
to help expert reviewers to evaluate whether a subtype belongs
below the new type or not, and whether the registration template
for a subtype contains the appropriate information. If the
criteria cannot be defined clearly, this is a strong indication
that whatever is being talked about is not suitable as a top-level
type.
* Any RFC defining a new top-level type MUST clearly document the
security considerations applying to all or a significant subset of
subtypes.
* At the minimum, one subtype MUST be described. A top-level type
without any subtype serves no purpose. Please note that the
'example' top-level describes a subtype 'example'.
3.7.2. Additional Considerations
Additional considerations for the definition of a new top-level type
include:
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* Existing wide use of an unregistered top-level type may be an
indication of a need, and therefore an argument for formally
defining a new top-level type. On the other hand, the use of
unregistered top-level types is highly discouraged.
* Use of an IETF Working Group to define a new top-level type is not
needed, but may be advisable in some cases. There are examples of
new top-level type definitions without a Working Group
([RFC2077]), with a short, dedicated WG ([RFC8081]), and with a
Working Group that included other related work
([I-D.ietf-mediaman-haptics]).
* The document defining the new top-level type should include
initial registrations of actual subtypes. The exception may be a
top-level type similar to 'example'. This will help to show the
need for the new top-level type, will allow checking the
appropriateness of the definition of the new top-level type, will
avoid separate work for registering an initial slate of subtypes,
and will provide examples of what is considered a valid subtype
for future subtype registrations.
* The registration and actual use of a certain number of subtypes
under the new top-level type should be expected. The existence of
a single subtype should not be enough; it should be clear that new
similar types may appear in the future. Otherwise, the creation
of a new top-level type is likely unjustified.
* The proposers of the new top-level type and the wider community
should be willing to commit to emitting and consuming the new top-
level type in environments that they control.
* The fact that a group of (potential) types have (mostly) common
parameters may be an indication that these belong under a common
new top-level type.
* Top-level types can help humans with understanding and debugging.
Therefore, evaluating how a new top-level type helps humans
understand types may be crucial.
* Common restrictions may apply to all subtypes of a top-level type.
Examples are the restriction to CRLF line endings for subtypes of
type 'text' (at least in the context of electronic mail), or on
subtypes of type 'multipart'.
* Top-level types are also used frequently in dispatching code. For
example "multipart/*" is frequently handled as multipart/mixed,
without understanding of a specific subtype. The top-level types
'image', 'audio', and 'video' are also often handled generically.
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Documents with these top-level types can be passed to applications
handling a wide variety of image, audio, or video formats. HTML
generating applications can select different HTML elements (e.g.
<img> or <audio>) for including data of different top-level types.
Applications can select different icons to represent unknown types
in different top-level types.
3.7.3. Negative Criteria
Negative indicators for creation of a new top-level type include:
* Media types are not a general type system. A top-level type MUST
NOT be defined if its main or only purpose is to map other type
systems, protocol elements, or registration spaces. Examples of
such discouraged uses include mapping media types to programming
language primitives, ontologies, object identifiers, URIs and URI
schemes, and file extensions. That said, media types MAY use
parameters to carry such information. For example, information on
a file extension '.dcat' can be encoded as 'application/octet-
string; filename=foo.dcat'.
* A new top-level type SHOULD NOT generate aliases for existing
widely used types or subtypes.
* Top-level types with an "X-" prefix cannot be registered, and
SHOULD NOT be used. See [RFC6648].
4. Media Subtypes
4.1. Registration Trees
To increase the efficiency and flexibility of the registration
process, different structures of subtype names can be registered in
"trees," distinguished with faceted name prefixes.
For example, a subtype that is recommended for wide support and
implementation by the Internet community would be registered in the
standards tree and not have a prefix, while a subtype that is used to
move files associated with proprietary software would be registered
in the vendor tree, and so its name would begin with a "vnd." prefix.
Note that some previously defined media types do not conform to the
naming conventions described below; see Appendix B.
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4.1.1. Standards Tree
The standards tree is intended for those media types that require a
substantive review and approval process in a recognized standards-
related organization. For media types that do not require such a
process, see the vendor and personal trees.
Registrations in the standards tree MUST be either:
1. approved directly by the IESG (in the case of registrations
associated with IETF specifications, ), or
2. registered by a recognized standards-related organization using
the "Specification Required" IANA registration policy Section 4.6
of [RFC8126] (which implies Expert Review), or
3. approved by the Designated Expert(s) as identifying a "community
format", as described in Section 4.1.1.1.
The first procedure is used for registrations from IETF Consensus
documents, or in rare cases when registering a grandfathered (see
Appendix B) and/or otherwise incomplete registration is in the
interest of the Internet community. See Section 2.2 for publication
requirements.
In the second case, the IESG makes a one-time decision on whether the
registration submitter represents a recognized standards-related
organization; after that, registration requests are performed as
specified in Section 5.3. The format MUST be described by a formal
specification produced by the submitting standards-related
organization.
The third case is described in Section 4.1.1.1.
Media types in the standards tree MUST NOT have faceted names, unless
they are grandfathered in using the process described in Appendix B.
The change controller of a media type registered in the standards
tree is assumed to be the standards-related organization itself.
Modification or alteration of the specification uses the same level
of processing (e.g., a registration submitted on Standards Track can
be revised in another Standards Track RFC, but cannot be revised in
an Informational RFC) required for the initial registration.
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4.1.1.1. Community Formats in the Standards Tree
Some formats are interoperable (i.e., they are supported by more than
one implementation), but their specifications are not published by a
recognized standards-related organization. To accommodate these
cases, the Designated Expert(s) are empowered to approve
registrations in the standards tree that meet the following criteria:
* There is a well-defined specification for the format
* That specification is not tied to or heavily associated with one
implementation
* The specification is freely available at a stable location
* There are multiple interoperable implementations of the
specification, or they are likely to emerge
* The requested name is appropriate to the use case, and not so
generic that it may be considered 'squatting'
* There is no conflict with IETF work or work at other recognised
SDOs (present or future)
* There is evidence of broad adoption
The Designated Expert(s) have discretion in applying these criteria;
in rare cases, they might judge it best to register an entry that
fails one or more.
Note that such registrations still go through preliminary community
review (Section 5.1), and decisions can be appealed (Section 5.3).
4.1.2. Vendor Tree
The vendor tree is intended for media types associated with publicly
available products. "Vendor" and "producer" are construed very
broadly in this context, and are considered equivalent.
A registration may be placed in the vendor tree by anyone who needs
to interchange files associated with some product or set of products.
However, the registration properly belongs to the vendor or
organization producing the software that employs the type being
registered, and that vendor or organization can at any time elect to
assume change control of a registration done by a third party in
order to correct or update it. See Section 5.5 for additional
information.
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When a third party registers a type on behalf of someone else, both
entities SHOULD be noted in the Change Controller field in the
registration. One possible format for this would be "Foo, on behalf
of Bar".
Vendor tree registrations are 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 are not required, requesting review on the media-
types@ietf.org mailing list is encouraged, to improve the quality of
those specifications.
Registrations in the vendor tree may be submitted directly to the
IANA, where they will undergo Expert Review Section 4.5 of [RFC8126]
prior to approval.
4.1.3. Personal Tree
The personal tree is intended for media types created experimentally
or as part of products that are not distributed commercially. This
tree is sometimes referred to as the "vanity" tree.
Personal tree registrations are distinguished by the leading facet
"prs.".
The change controller of a "personal" registration 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 are not required, requesting review on the media-
types@ietf.org mailing list is encouraged, to improve the quality of
those specifications.
Registrations in the personal tree may be submitted directly to the
IANA, where they will undergo Expert Review Section 4.5 of [RFC8126]
prior to approval.
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4.1.4. Unregistered x. Tree
Subtype names with "x." as the first facet are intended exclusively
for use in private, local environments. Subtypes using this tree
cannot be registered and are intended for use only with the active
agreement of the parties exchanging them.
The low barrier to registration in the vendor and personal trees
means it should rarely, if ever, be necessary to use unregistered
types. Therefore, use of types in the "x." tree is strongly
discouraged.
Note that types with names beginning with "x-" are no longer
considered to be members of this tree (see [RFC6648]). Also note
that if a generally useful and widely deployed type incorrectly uses
an "x-" name prefix, it MAY be registered using its current name in
an alternative tree by following the procedure defined in Appendix B.
4.1.5. Additional Registration Trees
New top-level registration trees may be created by IETF Standards
Action.
It is explicitly assumed that these trees might be created for
external registration and management by well-known permanent
organizations; for example, scientific societies might 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 by a recognized standards-related organization.
When the IETF performs such review, it needs to consider the greater
expertise of the requesting organization with respect to the subject
media type.
4.2. Subtype Suffixes
[RFC6838] standardized a suffix convention for well-known structured
syntaxes. In particular, media types have been registered with
suffixes such as "+der", "+fastinfoset", and "+json".
A structured suffix is defined as all of the characters to the right
of the left-most "+" sign in a media type, including the left-most
"+" sign itself. The structured suffix MUST NOT contain more than
one "+" sign. As an example, given the "application/foo+bar" media
type: "application" is the top-level type, "foo" is the base subtype
name, and "+bar" is the structured suffix. A media type such as
"application/foo+bar+baz" is not allowed.
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The primary guideline for whether a structured type name suffix is
registrable is that it be described by a readily available
description, preferably within a document published by an established
standards-related organization, and for which there's a reference
that can be used in a Normative References section of an RFC.
Media types that make use of a named structured syntax SHOULD use the
appropriate registered "+suffix" for that structured syntax when they
are registered. By the same token, media types MUST NOT be given
names incorporating suffixes for structured syntaxes they do not
actually employ. "+suffix" constructs for as-yet unregistered
structured syntaxes SHOULD NOT be used, given the possibility of
conflicts with future suffix definitions.
Media types that make use of a named structured syntax, or similar
separator such as a dash "-", MUST ensure that the registration is
semantically aligned, from a data model perspective, with existing
base subtype names in the media type registry. For example, for the
media types "application/foo+bar" and "application/foo+baz", the
expectation is that the semantics suggested by the base subtype name
"application/foo" are the same between both media types. The
Designated Expert MUST reject a registration if they believe the
semantics for a media type registration does not align with existing
base subtype names in the media type registry.
Registrants MUST prove to the Designated Expert, such as through an
email to a public mailing list or issue tracker comment, that they
have consent from the existing change controller for the associated
base subtype name to register the new media type.
4.2.1. Common Suffix Patterns
There are a few common patterns that are utilized for media types
that use structured suffixes. These patterns include expressing that
the data associated with a media type:
* Utilizes a structured data format such as "+xml", "+json",
"+yaml", or "+cbor".
* Is compressed using a binary compression format such as "+zip" or
"+gzip".
* Is encoded in a digitally signature format such as "+jwt" or
"+cose".
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While it is conceivable that suffixes such as "+xml+zip" are
possible, such usage is NOT RECOMMENDED due to the large number of
combinatorial possibilities that could occur and the negative impact
that might have on security considerations for toolchains that
attempt to safely process all of the possibilities.
4.2.2. Fragment Identifiers and Suffixes
The syntax and semantics for fragment identifiers are specified in
the "Fragment Identifier Considerations" column in the IANA
Structured Syntax Suffixes registry. In general, when processing
fragment identifiers associated with a structured syntax suffix, the
following rules SHOULD be followed:
1. For cases defined for the structured syntax suffix, where the
fragment identifier does resolve per the structured syntax suffix
rules, then proceed as specified by the specification associated
with the "Fragment Identifier Considerations" column in the IANA
Structured Syntax Suffixes registry.
2. For cases defined for the structured syntax suffix, where the
fragment identifier does not resolve per the structured syntax
suffix rules, then proceed as specified by the specification
associated with the full media type.
3. For cases not defined for the structured syntax suffix, then
proceed as specified by the specification associated with the
full media type.
5. Media Type Registration Procedures
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.
Normal IETF processes need to 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 media-types@ietf.org
list as discussed below.
5.1. Preliminary Community Review
Notice of a potential media type registration in the standards tree
SHOULD be sent to the media-types@ietf.org mailing list for review.
Registrations in other trees MAY be sent to the list for review as
well; doing so is entirely OPTIONAL, but is strongly encouraged.
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The purpose of this notification 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 proposal or abandon the
registration completely and at any time.
5.2. Submit Request to IANA
Media types registered in the standards tree by the IETF itself MUST
be reviewed and approved by the IESG as part of the normal standards
process.
Standards-tree registrations by recognized standards-related
organizations as well as registrations in the vendor and personal
trees are submitted directly to the IANA, unless other arrangements
were made as part of a liaison agreement.
Registration requests can be sent to iana@iana.org. A web form for
registration requests is also available at:
http://www.iana.org/form/media-types
5.2.1. Provisional Registrations
Standardization processes often take considerable time to complete.
In order to facilitate prototyping and testing, it is often helpful
to assign media types early in the process. This way, identifiers
used during standards development can remain unchanged once the
process is complete, and implementations and documentation do not
have to be updated.
Accordingly, provisional registrations of media type names in the
standards tree MAY be submitted to IANA. The only required fields in
such registrations are the media type name and contact information
(including the standards-related organization name).
Upon receipt of a provisional registration, IANA will check the name
and contact information, then publish the registration in a distinct,
publicly-visible provisional registration list.
Provisional registrations MAY be updated or abandoned at any time.
When the registration is abandoned, the media type is no longer
registered in any sense; it can subsequently be registered just like
any other unassigned media type name.
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5.3. Review and Approval
With the exception of provisional standards-tree registrations,
registrations submitted to the IANA will be first given to the media
types reviewer, who is appointed by the IETF Applications Area
Director(s). The media types reviewer examines registration requests
to make sure they meet the requirements set forth in this document.
Decisions made by the media types reviewer may be appealed to the
IESG using the procedure specified in Section 6.5.4 of [RFC2026].
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.
In the case of standards-tree registrations from other standards-
related organizations, IANA will also check that the submitter is in
fact a recognized standards-related organization. If the submitter
is not currently recognized as such, the IESG will be asked to
confirm their status. Recognition from the IESG MUST be obtained
before a standards-tree registration can proceed.
5.4. Comments on Media Type Registrations
Comments on registered media types may be submitted by members of the
community to the IANA at iana@iana.org. These comments will be
reviewed by the media types reviewer and then passed on to the change
controller of the media type if possible.
Submitters of comments may request that their comment be attached to
the media type registration itself; if the IANA, in consultation with
the media types reviewer, approves, the comment will be made
accessible in conjunction with the type registration.
5.5. Change Procedures
Once a media type has been published by the IANA, the change
controller may request a change to its definition. The same
procedure that would be appropriate for the original registration
request is used to process a change request.
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.
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Significant changes to a media type's definition 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 change controller of a media type may pass responsibility to
another person or agency by informing the IANA; 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, fallen out of contact,
or is otherwise unable to make changes that are important to the
community.
5.6. Registration Template
Type name:
Subtype name:
Required parameters:
Optional parameters:
Encoding considerations:
Security considerations:
Interoperability considerations:
Published specification:
Applications that use this media type:
Fragment identifier considerations:
Additional information:
Deprecated alias names for this type:
Magic number(s):
File extension(s):
Macintosh file type code(s):
Person & email address to contact for further information:
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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:
Provisional registration? (standards tree only): Yes/No
(Any other information that the author deems interesting may be added
below this line.)
"N/A", written exactly that way, can be used in any field if desired
to emphasize the fact that it does not apply or that the question was
not omitted by accident. Do not use 'none' or other words that could
be mistaken for a response.
Limited-use media types should also note in the applications list
whether or not that list is exhaustive.
6. Structured Syntax Suffix Registration Procedures
Someone wishing to define a "+suffix" name for a structured syntax
for use with a new media type registration SHOULD:
1. Check IANA's registry of media type name suffixes to see whether
or not there is already an entry for that well-defined structured
syntax.
2. If there is no entry for their suffix scheme, fill out the
template (specified in Section 6.2) and include that with the
media type registration. The template may be contained in an
Internet Draft, alone or as part of some other protocol
specification. The template may also be submitted in some other
form (as part of another document or as a stand-alone document),
but the contents will be treated as an "IETF Contribution" under
the guidelines of BCP 78 [RFC5378].
3. Send a copy of the template or a pointer to the containing
document (with specific reference to the section with the
template) to the mailing list media-types@ietf.org, requesting
review. This may be combined with a request to review the media
type registration. Allow a reasonable time for discussion and
comments.
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4. Respond to review comments and make revisions to the proposed
registration as needed to bring it into line with the guidelines
given in this document.
5. Submit the (possibly updated) registration template (or pointer
to the document containing it) to IANA at iana@iana.org.
Upon receipt of a structured syntax suffix registration request,
1. IANA checks the submission for completeness; if sections are
missing or citations are not correct, IANA rejects the
registration request.
2. IANA checks the current registry for an entry with the same name;
if such a registry exists, IANA rejects the registration request.
3. IANA requests Expert Review of the registration request against
the corresponding guidelines.
4. The Designated Expert may request additional review or
discussion, as necessary.
5. If Expert Review recommends registration, IANA adds the
registration to the appropriate registry.
The initial registry content specification [RFC6839] provides
examples of structured syntax suffix registrations.
6.1. Change Procedures
Registrations may be updated in each registry by the same mechanism
as required for an initial registration. In cases where the original
definition of the scheme is contained in an IESG-approved document,
update of the specification also requires IESG approval.
6.2. Structured Syntax Suffix Registration Template
This template describes the fields that must be supplied in a
structured syntax suffix registration request:
Name
Full name of the well-defined structured syntax.
+suffix
Suffix used to indicate conformance to the syntax.
References
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Include full citations for all specifications necessary to
understand the structured syntax.
Encoding considerations
A full citation to a section in a specification that provides
general guidance regarding encoding considerations for any type
employing this syntax. The same requirements for media type
encoding considerations given in Section 2.6 apply here.
Interoperability considerations
A full citation to a section in a specification that documents any
issues regarding the interoperable use of types employing this
structured syntax should be given here. Examples would include
the existence of incompatible versions of the syntax, issues
combining certain charsets with the syntax, or incompatibilities
with other types or protocols.
Fragment identifier considerations
A full citation to a section in a specification that documents the
generic processing rules of fragment identifiers for any type
employing this syntax should be described here.
Security considerations
A full citation to a section in a specification that provides
security considerations shared by media types employing this
structured syntax must be specified here. The same requirements
for media type security considerations given in Section 2.8 apply
here, with the exception that the option of not assessing the
security considerations is not available for suffix registrations.
Contact
Person (including contact information) to contact for further
information.
Author/Change controller.
Person (including contact information) authorized to change this
suffix registration.
7. Security Considerations
Security requirements for both media type and media type suffix
registrations are discussed in Section 2.8.
8. IANA Considerations
_None Yet._
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9. Acknowledgments
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] [RFC4288]. 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.
Randy Bush, Francis Dupont, Bjoern Hoehrmann, Barry Leiba, Murray
Kucherawy, Alexey Melnikov, S. Moonesamy, Mark Nottingham, Tom
Petch, Peter Saint-Andre, and Jeni Tennison provided many helpful
review comments and suggestions.
10. References
10.1. Normative References
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
<https://www.rfc-editor.org/rfc/rfc2045>.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/rfc/rfc2046>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC2978] Freed, N. and J. Postel, "IANA Charset Registration
Procedures", BCP 19, RFC 2978, DOI 10.17487/RFC2978,
October 2000, <https://www.rfc-editor.org/rfc/rfc2978>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/rfc/rfc3629>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/rfc/rfc3986>.
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[RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007,
<https://www.rfc-editor.org/rfc/rfc4855>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/rfc/rfc5234>.
[RFC5378] Bradner, S., Ed. and J. Contreras, Ed., "Rights
Contributors Provide to the IETF Trust", BCP 78, RFC 5378,
DOI 10.17487/RFC5378, November 2008,
<https://www.rfc-editor.org/rfc/rfc5378>.
[RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized
Email Headers", RFC 6532, DOI 10.17487/RFC6532, February
2012, <https://www.rfc-editor.org/rfc/rfc6532>.
[RFC6648] Saint-Andre, P., Crocker, D., and M. Nottingham,
"Deprecating the "X-" Prefix and Similar Constructs in
Application Protocols", BCP 178, RFC 6648,
DOI 10.17487/RFC6648, June 2012,
<https://www.rfc-editor.org/rfc/rfc6648>.
[RFC6657] Melnikov, A. and J. Reschke, "Update to MIME regarding
"charset" Parameter Handling in Textual Media Types",
RFC 6657, DOI 10.17487/RFC6657, July 2012,
<https://www.rfc-editor.org/rfc/rfc6657>.
[RFC7303] Thompson, H. and C. Lilley, "XML Media Types", RFC 7303,
DOI 10.17487/RFC7303, July 2014,
<https://www.rfc-editor.org/rfc/rfc7303>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[RFC8179] Bradner, S. and J. Contreras, "Intellectual Property
Rights in IETF Technology", BCP 79, RFC 8179,
DOI 10.17487/RFC8179, May 2017,
<https://www.rfc-editor.org/rfc/rfc8179>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
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10.2. Informative References
[I-D.ietf-mediaman-haptics]
Muthusamy, Y. K. and C. Ullrich, "The 'haptics' Top-level
Media Type", Work in Progress, Internet-Draft, draft-ietf-
mediaman-haptics-05, 27 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-
mediaman-haptics-05>.
[MacOSUTIs]
Apple Computer, Inc., "Framework: Uniform Type
Identifiers", March 2024,
<https://developer.apple.com/documentation/
uniformtypeidentifiers>.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, DOI 10.17487/RFC2026, October 1996,
<https://www.rfc-editor.org/rfc/rfc2026>.
[RFC2048] Freed, N., Klensin, J., and J. Postel, "Multipurpose
Internet Mail Extensions (MIME) Part Four: Registration
Procedures", RFC 2048, DOI 10.17487/RFC2048, November
1996, <https://www.rfc-editor.org/rfc/rfc2048>.
[RFC2077] Nelson, S., Parks, C., and Mitra, "The Model Primary
Content Type for Multipurpose Internet Mail Extensions",
RFC 2077, DOI 10.17487/RFC2077, January 1997,
<https://www.rfc-editor.org/rfc/rfc2077>.
[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded
Word Extensions: Character Sets, Languages, and
Continuations", RFC 2231, DOI 10.17487/RFC2231, November
1997, <https://www.rfc-editor.org/rfc/rfc2231>.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", RFC 4288, DOI 10.17487/RFC4288,
December 2005, <https://www.rfc-editor.org/rfc/rfc4288>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/rfc/rfc6838>.
[RFC6839] Hansen, T. and A. Melnikov, "Additional Media Type
Structured Syntax Suffixes", RFC 6839,
DOI 10.17487/RFC6839, January 2013,
<https://www.rfc-editor.org/rfc/rfc6839>.
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[RFC8081] Lilley, C., "The "font" Top-Level Media Type", RFC 8081,
DOI 10.17487/RFC8081, February 2017,
<https://www.rfc-editor.org/rfc/rfc8081>.
[RFC8187] Reschke, J., "Indicating Character Encoding and Language
for HTTP Header Field Parameters", RFC 8187,
DOI 10.17487/RFC8187, September 2017,
<https://www.rfc-editor.org/rfc/rfc8187>.
[windowsClipboardNames]
MicroSoft Inc., "Clipboard Formats", August 2020,
<https://learn.microsoft.com/en-us/windows/win32/dataxchg/
clipboard-formats>.
Appendix A. 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 is now a 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
specification incorporates such restrictions into media type
registrations in a systematic way. See Section 2.10 for additional
discussion.
Appendix B. Grandfathered Media Types
A number of media types with unfaceted subtype names, registered
prior to 1996, would, if registered under the guidelines in this
document, be given a faceted name and 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.
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From time to time there may also be cases where a media type with an
unfaceted subtype name has been widely deployed without being
registered. (Note that this includes subtype names beginning with
the "x-" prefix.) If possible, such a media type SHOULD be
reregistered with a proper faceted subtype name, possibly using a
deprecated alias to identify the original name (see Section 2.4.1).
However, if this is not possible, the type can, subject to approval
by both the media types reviewer and the IESG, be registered in the
proper tree with its unfaceted name.
Authors' Addresses
Mark Nottingham
Cloudflare
Prahran
Australia
Email: mnot@mnot.net
URI: https://www.mnot.net/
Pete Resnick
Email: resnick@episteme.net
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