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Media Type Maintenance Internet-Draft This document defines procedures for the specification and registration of media types for use in HTTP, MIME, and other Internet protocols. It obsoletes and . Note that is also part of BCP 13, and addresses registration of MIME External Body Access Types and Transfer Encodings. About This Document Status information for this document may be found at . information can be found at . Source for this draft and an issue tracker can be found at .

Introduction Internet application protocols (including but not limited to HTTP and MIME ) are capable of carrying arbitrary labeled content. Those labels are known as media types. A media type consists of a top-level type () and a subtype (), which is further structured into a tree (identified by a prefix). A subtype can also be associated with a structured syntax (identified by suffix). Optionally, a media type can be defined to allow companion data, known as parameters. defines the criteria for registering media types. outlines the procedures used to do so. The location of the media type registry is:

• https://www.iana.org/assignments/media-types/

outlines the procedures for managing the registry for structured syntax suffixes. It is located at:

• https://www.iana.org/assignments/media-type-structured-suffix/

Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. RFC 2119 language is used to describe the requirements placed upon the registrant in the registration process. This specification makes use of the Augmented Backus-Naur Form (ABNF) notation, including the core rules defined in Appendix B of that document.

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 (). 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, and does not indicate that the specification is adequate for any particular purpose. Additional requirements specific to the registration of XML media types are specified in .

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 , base64 cannot be registered as a media type. This requirement applies regardless of the registration tree involved.

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 needs to 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 needs to be referenced by it. See for further discussion of "permanent and readily available." 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.

Intellectual Property The registration of media types involving patented technology is permitted. However, the restrictions set forth in BCP 79 and BCP 78 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.

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. 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. Universal support and implementation of a media type are not a requirement for registration. The requirement and recommendations in this subsection apply regardless of the registration tree involved.

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: Note that this syntax is more restrictive than what is allowed by or . Also note that while this syntax allows type and subtype 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 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 . 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.

Parameters Media types can 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: Note that this syntax is more restrictive than what is allowed by the ABNF in and amended by . 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 needs to be specified upon registration. Additionally, some transports impose restrictions on parameter value syntax, so care needs to be taken to limit the use of potentially problematic syntaxes; for example, binary-valued parameters, while permitted in some protocols, are best avoided. Some parameters are reused across multiple media type definitions to provide common functionality. For example, the 'Codecs' and 'Profiles' Parameters for "Bucket" Media Types identify media codecs used inside the container and their parameters. RTP payload formats have several common parameters: see , and . Note that a protocol can impose further restrictions on parameter value syntax, depending on how it chooses to represent parameters. MIME allows binary parameters as well as parameter values expressed in a specific charset, but other protocols may be less flexible. For example, HTTP obsoletes field values containing characters outside the ASCII range (), requiring field definitions to use encoding mechanisms like to support other characters. Media types registered in the standards tree MUST NOT subsequently add backwards-incompatible functionality through the addition of parameters. New parameters MAY be used to convey additional information so long as their processing is backwards-compatible, so that existing implementations can still handle the message successfully. Media types registered in the vendor and personal trees SHOULD NOT violate this requirement. Changes to parameters (including the introduction of new ones) is managed in the same manner as other changes to the media type; see .

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 specify the nature of the data a media type contains 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 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 .

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

Fragment Identifiers Media type registrations can specify how applications should interpret fragment identifiers (specified in ) associated with the media type. Requirements for media types that use a structured syntax suffix are given in . Media types are encouraged to adopt fragment identifier schemes that are used with semantically similar media types.

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 need to 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 need to 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 can be extended by use of the "comments on media types" mechanism described in below. Issues that need to be described in a security analysis of a media type include:

• Processing of complex media types might modify or delete a recipient's files or trigger actions on other resources. If unrestricted, this could have devastating effects. See the registration of the application/postscript media type in 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 to be taken by applications) 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 designed for applications that require an assurance of security without providing that assurance. 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.

Intended Usage The "Intended usage" field in the registration template MUST contain one of "COMMON", "LIMITED USE", or "OBSOLETE". Registrations intended for general use should be registered as COMMON. LIMITED USE accommodates media types that are only intended to be used in closed or specialized systems. OBSOLETE indicates that the media type should no longer be used. Limited-use media types should also note in the applications list whether or not that list is exhaustive. The "Restrictions on usage" field can convey additional information about restrictions on where the media type can be used.

Contact Information The registration template contains distinct fields for contact information:

• The "Person to contact for further information" is intended to be used by those with questions about the media type and its use. This might be an individual with technical knowledge or a support address.
• The "Author" is the person(s) to be attributed with creation of the media type specification.
• The "Change controller" is the party who will authorise any future changes to the status or details of the registration.

Each should contain a name (of a person or other entity) and e-mail address. Optionally, they may also include a URL. All three are required.

Additional Information The following optional information should be included in the specification of a media type if it is available:

• Deprecated Aliases. In some cases, a single media type may have been widely deployed using multiple names prior to registration. In such cases, a preferred name MUST be chosen for the media type, and applications are required to use this to be compliant with the type's registration. However, a list of deprecated aliases by which the type is known can be supplied as additional information in order to assist applications in processing the media type properly.
• Magic number(s) (length, octet values). Magic numbers are byte sequences that are always present at a given place in the file, and can be used to identify it 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 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 for definitions and syntax).

When registering a media type in the standards tree, specification authors can provide this information in the formal specification of the format, by incorporating the IANA media type registration form into the specification itself.

Top-Level Media Types The list of top-level types is maintained in the IANA Top-Level Media Types registry at:

• https://www.iana.org/assignments/top-level-media-types/

Top-level types can place various restrictions on the media types that use them. New media types MUST conform to the restrictions (if any) of their top-level type.

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 top-level type can be defined to accommodate it. Registration of a new top-level type requires Standards Action in the IETF and, hence, the publication of a RFC on the Standards Track. For formats that do not fit below any other top-level type, the 'application' top-level type can always be used. The main function of media types and subtypes is the dispatch of data formats to application code. In most cases, this requires and is done using the full type (i.e., including the subtype, and often some parameters). The top-level type can occasionally serve as a fallback for the tentative dispatch to applications handling a very wide range of related formats.

Required Criteria Definitions of new top-level types MUST fulfil the following criteria:

• The top-level type is defined in a Standards Track RFC (see ). This will make sure there is sufficient community interest, review, and consensus.
• The IANA Considerations section of that RFC requests 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 are defined clearly. This will help the Designated Expert(s) 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.
• The RFC defining the top-level type states how recipients should handle unrecognised subtypes.
• The RFC clearly documents security considerations applying to all or a significant subset of subtypes.
• At the minimum, one subtype (not including a potential 'example' subtype) is described. A top-level type without any subtype serves no purpose. The only exception is the 'example' top-level type, which disallows registration of subtypes.

Additional Considerations Additional considerations for the definition of a new top-level type include:

• 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 (), with a short, dedicated WG (), and with a Working Group that included other related work ().
• 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, allow for checking the appropriateness of the new top-level type's definition, avoid redundant work in registering an initial slate of subtypes, and provide examples of valid subtypes for future 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. 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.

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 whose main or only purpose is to map other type systems, protocol elements, or registration spaces MUST NOT be defined. 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 can 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 .

Media Subtypes

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 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 subtype name would begin with a "vnd." prefix.

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 (as defined by https://www.iana.org/assignments/iesg-recognized-organizations). For media types that do not require such a process, see the vendor and personal trees. Registrations in the standards tree are either:

1. approved directly by the IESG, or
2. registered by a recognized standards-related organization using the "Specification Required" IANA registration policy (which implies Expert Review), or
3. approved by the Designated Expert(s) as identifying a "community format", as described in .

The first procedure is used for registrations from IETF consensus documents on the IETF stream, and can be used for RFCs from other streams. 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 . The third case is described in . Media types registered by the IETF in the standards tree MUST be published as RFCs. Standards-tree registrations for media types defined by other standards-related organizations MUST be described by a formal specification produced by that organization. Note that in both cases, the early allocation process described in is available. Media types cannot be registered in the standards tree with faceted subtype names, but note that some pre-existing types do use them. The change controller of a media type registered in the standards tree is assumed to be the standards-related organization itself. In the case of IETF standards and community formats (see ), the change controller is normally the IETF. 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.

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:

• The specification is well-defined and complete
• The specification is freely available to the public at a permanent and readily available location
• The specification is not tied to or heavily associated with one implementation
• There are multiple interoperable implementations of the specification, or such implementations are likely to emerge
• There is evidence of broad adoption
• The use case addressed by the specification is using media types appropriately
• The requested value is appropriate to the use case, and not so generic that it may be considered 'squatting'

The Designated Expert(s) have discretion in applying these criteria; in some cases, they might judge it best to register an entry that fails one or more. The intent is to assure that successfully deployed community formats have registered media types. As such, the criteria above are designed to preclude anticipatory registrations. Note that such registrations still go through preliminary community review (), and decisions can be appealed ().

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 data 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 for additional information. 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 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 per prior to approval.

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 per prior to approval.

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 subtype names beginning with "x-" are no longer considered to be members of this tree (see ). Also note that if a generally useful and widely deployed type incorrectly uses an "x-" subtype name prefix, it can be registered in an alternative tree by following the procedure defined in .

Additional Registration Trees New registration trees may be created by IETF Standards Action. No such new registrations are currently envisioned.

Structured Syntax Suffixes Media types can be identified as using a well-known structured syntax (for example, XML or JSON) with a "+suffix" convention. A structured syntax suffix is defined as all of the characters to the right of the right-most "+" character in a media type, including the right-most "+" character itself. A structured syntax suffix MUST NOT contain more than one "+" character. For example, in the "application/foo+bar" media type "application" is the top-level type, "foo" is the subtype name, and "+bar" is the structured syntax suffix. A media type such as "application/foo+bar+baz" is not registrable, but if it is nevertheless used, its suffix is "+baz". Structured syntax suffixes MUST be registered before use; see . Media types that make use of a structured syntax SHOULD use the appropriate suffix, and MUST NOT use suffixes for structured syntaxes that they do not actually employ. Media types that make use of a structured syntax, or similar separator such as a dash "-", SHOULD be semantically aligned, from a data model perspective, with existing 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 subtype name "application/foo" are the same between both media types. Registrations are expected to align with existing subtype or suffix names in the media type registry; see . A party requesting registration of a media type that adds a suffix to an existing subtype is expected to coordinate with the change controller(s) for the already registered media type.

Use Cases Common use cases for media types that employ structured syntax suffixes include:

• Identifying use of a structured data format; for example "+xml", "+json", "+yaml", and "+cbor"
• Flagging compression with a format such as "+zip" or "+gzip"
• Flagging encoding in a digital signature format such as "+jwt" or "+cose"

While it might be desirable to use a compound suffix (e.g., "+xml+zip"), experience shows that suffixes are a poor means of indicating more than one such convention; the combinations of suffixes quickly multiply, and there is not a well-specified processing model that can handle them safely. Therefore, multiple suffixes are disallowed from use.

Fragment Identifiers and Structured Syntax Suffixes A structured syntax suffix registration can specify fragment identifier syntax and semantics, recorded in the "Fragment Identifier Considerations" column of the Structured Syntax Suffixes registry. Where a suffix does so, a media type using that suffix MUST specify fragment identifier handling that is consistent with the suffix's, and MUST NOT disallow syntax that the suffix requires. Otherwise, fragment identifier handling is determined by the media type.

Security Considerations for Structured Syntax Suffix Processing Processors of the information in structured syntax suffixes encounter the following security considerations.

Relationships Between Types The relationship between a media type that employs a structured syntax suffix and the type (if any) that results from removing that suffix cannot be known merely by examining the types. For example, content marked "application/foo+bar" may or may not be processable or valid as "application/foo" content. It may be possible to derive one from the other, but that is specific to the structured syntax suffix and/or media type itself. This uncertainty extends to fragment identifier processing: per the rules in , a fragment identifier that might be valid for an "application/foo+bar" document might not be applicable to another "+bar" document, because media-type specific fragment identifier resolution might be used. Likewise, the security characteristics that a processor needs to consider may change depending upon whether it is solely processing the structured syntax suffix or the entire media type. For example, a processor cannot presume that the security characteristics for a "application/baz+bar" document will be the same as for a "application/foo+bar" document.

Partial Processing An attacker might append structured syntax suffixes in order to trick processors into skipping security checks. For example, an attacker might use an "application/vnd.ms-excel.addin.macroEnabled.12+zip" structured syntax suffix to trigger an unzip process into invoking Microsoft Excel, bypassing anti-virus scanners that would normally block the file from being opened. Enterprising attackers might take advantage of toolchains that partially process media types in this manner. Processing of media types based only on the presence of a structured syntax suffix needs to ensure that further processing does not blindly trust the decoded data. For example, proper magic header or file structure checking could mitigate this attack.

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.

Preliminary Community Review Notice of a potential media type registration in the standards tree MUST be sent to the media-types@ietf.org mailing list for review. Registrations in other trees can be sent to the list for review as well; doing so is entirely optional, but is strongly encouraged. 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 at any time.

Submit Request to IANA Standards tree registrations by the IETF itself are submitted by the IESG as part of the normal standards process. Standards-tree registrations by recognized standards-related organizations are submitted directly to the IANA, unless other arrangements were made as part of a liaison agreement. Standards-tree registrations using the community format process () are submitted by the Designated Expert(s) to IANA. Registrations in the vendor and personal trees are submitted directly to the IANA. Registration requests can be submitted to iana@iana.org. A web form for registration request submission is also available at:

• https://www.iana.org/form/media-types

Review and Approval Registrations submitted to the IANA will be first given to the Designated Expert(s), who are appointed by the IESG. When a suffix is present in a registration, IANA will inform the expert:

• If the suffix is not registered, noting whether a suffix registration request accompanies the media type registration (see )
• Of any registered media types that have the same type and subtype with a different suffix, including those where the proposed suffix is absent (see for an example)

Because structured syntax suffixes are required to be registered before use (), a media type registration whose suffix is unregistered cannot be approved. When a suffix registration request accompanies it, the Designated Expert(s) are expected to hold the media type registration until the suffix is registered; otherwise, they are expected to ask the requester to register the suffix, choose a different subtype name, or withdraw the request. 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 needs to be obtained before a standards-tree registration can proceed. The Designated Expert(s) will examine registration requests to make sure they meet the requirements set forth in this document. Decisions made by the Designated Expert(s) may be appealed to the IESG using the procedure specified in . 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.

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 Designated Expert(s) 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 Designated Expert(s), approves, the comment will be made accessible in conjunction with the type registration.

Change Procedures When a change to a media type registration is requested, the applicable registration procedure for that media type's tree is used to process the request. Changes may be requested by the change controller, or by other parties if IANA verifies that the change controller approves the change. 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 usage" field (see ). Significant changes to a media type's definition should be requested only when there are serious omissions or errors in the published specification. 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. If the Designated Expert(s) find that the change controller is unresponsive or uncontactable for a reasonable period of time and reasonable efforts have been made to contact the change controller, they may recommend to the IESG that the change controller be updated.

Registration Template

Type name:

[see ]

Subtype name:

[see ]

Required parameters:

[see ]

Optional parameters:

[see ]

Encoding considerations:

[see ]

Security considerations:

[see ]

Interoperability considerations:

[see ]

Published specification:

[see ]

Applications that use this media type:

Fragment identifier considerations:

[see ]

Additional information: [see ]

Deprecated alias names for this type: Magic number(s): File name extension(s): macOS Uniform Type Identifier(s): Windows clipboard name(s):

Person & email address to contact for further information:

[see ]

Intended usage:

[see ]

Restrictions on usage:

[see ]

Author:

[see ]

Change controller:

[see ]

(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.

Structured Syntax Suffix Registration Procedures Structured syntax suffixes must be described by a readily available description, preferably within a document published by an established standards-related organization, for which there's a reference that can be used in a Normative References section of an RFC. Someone wishing to define a "+suffix" name for a structured syntax for use with a new media type registration should:

1. Check the IANA registry of media type name suffixes to determine if an entry already exists for that structured syntax.
2. If there is no corresponding entry, fill out the template (see ) and include that with the media type registration request. 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, but the contents will be treated as an "IETF Contribution" under the guidelines of BCP 78 .
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.
4. Respond to review comments and make revisions to the proposed registration as needed.
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 provides examples of structured syntax suffix registrations.

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.

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

A citation for all specifications necessary to understand the structured syntax.

Encoding considerations

A citation to a section in a specification that provides general guidance regarding encoding considerations for any type employing this syntax. The requirements for media type encoding considerations given in apply.

Interoperability considerations

A citation to a section in a specification that documents any issues regarding the interoperable use of types employing this structured syntax. For example, 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 citation to a section in a specification that documents the generic processing rules of fragment identifiers for any type employing this syntax.

Security considerations

A citation to a section in a specification that provides security considerations shared by media types employing this structured syntax. The security considerations for a media type registration in the standards tree (per ) apply.

Contact

Person (including contact information) to contact for further information.

Author/Change controller

Person (including contact information) authorized to change this suffix registration.

Security Considerations Security considerations for media types are discussed in . Security Considerations for structured suffix processing is discussed in .

IANA Considerations

Top-Level Types Registry In the Top-Level Media Types registry, IANA should link the reference field for each top-level type to the specific subsection in question, rather than just the relevant RFC. The following entries should have the corresponding comment edits:

• text — append to the existing comment: "New registrations must specify how the charset is determined; where a charset parameter is defined it must name a charset registered per RFC 2978; UTF-8 is the recommended default."
• multipart and message — "Subtypes must conform to the syntax rules and other requirements of RFC 2046, as amended by Section 3.5 of RFC 6532."

Additionally, RFC 6532 should be added to the Reference column for multipart and message.

Structured Syntax Suffixes Registry Thirteen entries in the Structured Syntax Suffixes registry -- "+json", "+ber", "+cbor", "+der", "+fastinfoset", "+wbxml", "+zip", "+tlv", "+json-seq", "+sqlite3", "+jwt", "+gzip", and "+cbor-seq" -- describe fragment identifier processing with a three-case rule that has been copied between registrations since . Each of those entries also records that no fragment identifier syntax is defined for the suffix in question, so those cases cannot arise; now specifies how fragment identifiers interact with structured syntax suffixes. IANA should remove that three-case text from the "Fragment Identifier Considerations" field of those entries, retaining their remaining content, and work with the Experts and the IESG as appropriate.

Recognized Standards-Related Organizations IANA should notify recognized standards-related organizations when this document is published (where feasible), and highlight the need to consider how their processes interact with the registration procedure (see, e.g., https://www.w3.org/guide/editor/mediatypes.html#registration-process).

Provisional Registrations This revision removes provisional registrations from the standards tree. Accordingly, IANA should remove that information from the registry and work with the Experts and the IESG as appropriate to identify an appropriate disposition for registrations that are marked as 'provisional'.

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 . 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.

Contributors Much of the text of this document is directly taken from and . We acknowledge the following authors of those documents as contributors to this: Ned Freed John C. Klensin 1770 Massachusetts Ave, #322 Cambridge, MA 02140 USA EMail: john+ietf@jck.com Tony Hansen AT&T Laboratories 200 Laurel Ave. Middletown, NJ 07748 USA EMail: tony+mtsuffix@maillennium.att.com Martin J. Dürst Aoyama Gakuin University Fuchinobe 5-10-1, Chuo-ku, Sagamihara, Kanagawa 252-5258 Japan Phone: +81 42 759 6329 Email: duerst@it.aoyama.ac.jp URI: https://www.sw.it.aoyama.ac.jp/Dürst/

References Normative References Internet Assigned Numbers Authority Internet Assigned Numbers Authority Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the fourth edition of this document; it obsoletes RFC 8126. Internet Assigned Numbers Authority Internet Assigned Numbers Authority This document describes the requirements for securing IANA code point assignments for IETF Stream Internet-Drafts and specifications being drafted by other standards-related organizations. This document obsoletes RFC 7120. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. This initial document specifies the various headers used to describe the structure of MIME messages. [STANDARDS-TRACK] In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK] This specification standardizes three media types -- application/xml, application/xml-external-parsed-entity, and application/xml-dtd -- for use in exchanging network entities that are related to the Extensible Markup Language (XML) while defining text/xml and text/ xml-external-parsed-entity as aliases for the respective application/ types. This specification also standardizes the '+xml' suffix for naming media types outside of these five types when those media types represent XML MIME entities. The IETF policies about Intellectual Property Rights (IPR), such as patent rights, relative to technologies developed in the IETF are designed to ensure that IETF working groups and participants have as much information as possible about any IPR constraints on a technical proposal as early as possible in the development process. The policies are intended to benefit the Internet community and the public at large, while respecting the legitimate rights of IPR holders. This document sets out the IETF policies concerning IPR related to technology worked on within the IETF. It also describes the objectives that the policies are designed to meet. This document updates RFC 2026 and, with RFC 5378, replaces Section 10 of RFC 2026. This document also obsoletes RFCs 3979 and 4879. The IETF policies about rights in Contributions to the IETF are designed to ensure that such Contributions can be made available to the IETF and Internet communities while permitting the authors to retain as many rights as possible. This memo details the IETF policies on rights in Contributions to the IETF. It also describes the objectives that the policies are designed to meet. This memo obsoletes RFCs 3978 and 4748 and, with BCP 79 and RFC 5377, replaces Section 10 of RFC 2026. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document specifies the procedure to register RTP payload formats as audio, video, or other media subtype names. This is useful in a text-based format description or control protocol to identify the type of an RTP transmission. [STANDARDS-TRACK] This second document defines the general structure of the MIME media typing system and defines an initial set of media types. [STANDARDS-TRACK] A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK] Historically, designers and implementers of application protocols have often distinguished between standardized and unstandardized parameters by prefixing the names of unstandardized parameters with the string "X-" or similar constructs. In practice, that convention causes more problems than it solves. Therefore, this document deprecates the convention for newly defined parameters with textual (as opposed to numerical) names in application protocols. This memo documents an Internet Best Current Practice. Informative References Apple Computer, Inc. Microsoft Corporation This document defines procedures for the specification and registration of media types for use in HTTP, MIME, and other Internet protocols. This memo documents an Internet Best Current Practice. This document defines best practices for defining new top-level media types. It also introduces a registry for top-level media types, and contains a short history of top-level media types. It updates RFC 6838. This document specifies IANA registration procedures for MIME external body access types and content-transfer-encodings. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document defines procedures for the specification and registration of media types for use in MIME and other Internet protocols. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This memo defines extensions to the RFC 2045 media type and RFC 2183 disposition parameter value mechanisms. This memo also defines an extension to the encoded words defined in RFC 2047 to allow the specification of the language to be used for display as well as the character set. [STANDARDS-TRACK] Several MIME type/subtype combinations exist that can contain different media formats. A receiving agent thus needs to examine the details of such media content to determine if the specific elements can be rendered given an available set of codecs. Especially when the end system has limited resources, or the connection to the end system has limited bandwidth, it is helpful to know from the Content- Type alone if the content can be rendered. This document specifies two parameters, 'codecs' and 'profiles', that are used with various MIME types or type/subtype combinations to allow for unambiguous specification of the codecs employed by the media formats contained within, or the profile(s) of the overall container format. This document obsoletes RFC 4281; RFC 4281 defines the 'codecs' parameter, which this document retains in a backwards compatible manner with minor clarifications; the 'profiles' parameter is added by this document. By labeling content with the specific codecs indicated to render the contained media, receiving systems can determine if the codecs are supported by the end system, and if not, can take appropriate action (such as rejecting the content, sending notification of the situation, transcoding the content to a supported type, fetching and installing the required codecs, further inspection to determine if it will be sufficient to support a subset of the indicated codecs, etc.). Similarly, the profiles can provide an overall indication, to the receiver, of the specifications with which the content complies. This is an indication of the compatibility of the container format and its contents to some specification. The receiver may be able to work out the extent to which it can handle and render the content by examining to see which of the declared profiles it supports, and what they mean. [STANDARDS-TRACK] In this specification, we define a framework for specifying restrictions on RTP streams in the Session Description Protocol (SDP). This framework defines a new "rid" ("restriction identifier") SDP attribute to unambiguously identify the RTP streams within an RTP session and restrict the streams' payload format parameters in a codec-agnostic way beyond what is provided with the regular payload types. This specification updates RFC 4855 to give additional guidance on choice of Format Parameter (fmtp) names and their relation to the restrictions defined by this document. By default, header field values in Hypertext Transfer Protocol (HTTP) messages cannot easily carry characters outside the US-ASCII coded character set. RFC 2231 defines an encoding mechanism for use in parameters inside Multipurpose Internet Mail Extensions (MIME) header field values. This document specifies an encoding suitable for use in HTTP header fields that is compatible with a simplified profile of the encoding defined in RFC 2231. This document obsoletes RFC 5987. Mitra The purpose of this memo is to propose an update to Internet RFC 2045 to include a new primary content-type to be known as "model". [STANDARDS-TRACK] This memo serves to register and document the "font" top-level media type, under which subtypes for representation formats for fonts may be registered. This document also serves as a registration application for a set of intended subtypes, which are representative of some existing subtypes already in use, and currently registered under the "application" tree by their separate registrations. This memo registers and documents the 'haptics' top-level media type, under which subtypes for representation formats for haptics may be registered. This document also serves as a registration for a set of subtypes, which are representative of some existing subtypes already in use. This memo documents the process used by the Internet community for the standardization of protocols and procedures. It defines the stages in the standardization process, the requirements for moving a document between stages and the types of documents used during this process. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. A content media type name sometimes includes partitioned meta- information distinguished by a structured syntax to permit noting an attribute of the media as a suffix to the name. This document defines several structured syntax suffixes for use with media type registrations. In particular, it defines and registers the "+json", "+ber", "+der", "+fastinfoset", "+wbxml" and "+zip" structured syntax suffixes, and provides a media type structured syntax suffix registration form for the "+xml" structured syntax suffix. This document is not an Internet Standards Track specification; it is published for informational purposes. This set of documents, collectively called the Multipurpose Internet Mail Extensions, or MIME, redefines the format of messages. This fourth document, RFC 2048, specifies various IANA registration procedures for some MIME facilities. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.

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 , 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 .

Changes from RFC 6838 This document incorporates the following significant changes:

• Incorporation of RFC 9694: This revision obsoletes RFC 9694 and integrates its requirements into the media type registration template.
• RFC 6838's "Macintosh file type code(s)" template field is now "macOS Uniform Type Identifier(s)" ().
• The notice requirement in went from SHOULD to MUST.
• Removal of Provisional Registrations: This revision removes the concept of "provisional registrations" from the standards tree.
• Expansion of the Standards Tree (Community Formats): A new process is defined allowing the Designated Expert(s) to approve registrations in the standards tree for "community formats." ().
• Strict Suffix Constraints: This revision updates structured syntax suffixes to disallow those containing more than one "+" character ().
• Change Controller Updates: In cases where a change controller is unresponsive or uncontactable, this revision empowers the Designated Expert(s) to recommend to the IESG that the change controller be updated ().
• Top-Level Type Guidance: This revision adds criteria for evaluating the creation of new top-level types ().